Multimessenger Astronomy

This gallery brings together animations, visualizations, videos and still images relating to the growing field of “multimessenger” astronomy.

In the past century, humans have mastered how to detect light beyond what our eyes can see — unveiling secrets held in other parts of the electromagnetic spectrum. More recently, we have developed detectors for other signals from the universe — particles ejected from black holes and other high-energy sources and even wiggles of space-time in the form of gravitational waves. This new capability of combining information from all of these different messengers to more completely understand a source is called multimessenger astronomy.

The four messengers astronomers study are light in all its forms, cosmic rays, neutrinos, and gravitational waves.

When an astronomical source varies slowly, astronomers can combine information from different messengers received at different times — sometimes even years apart — and still get a good picture of it. But many source types change rapidly with time. For them, it’s critical that observations occur simultaneously or within a short time span so that astronomers capture the properties of different messengers before the source changes. Astronomers call this “time domain” astronomy. Multimessenger time domain astronomy is a powerful new tool for exploring the cosmos.

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Going multimessenger

Light

  •
    The Electromagnetic Spectrum
    2016.09.20
    The electromagnetic (EM) spectrum is the range of all types of EM radiation. Radiation is energy that travels and spreads out as it goes – the visible light that comes from a lamp in your house and the radio waves that come from a radio station are two types of electromagnetic radiation. The other types of EM radiation that make up the electromagnetic spectrum are microwaves, infrared light, ultraviolet light, X-rays and gamma-rays.
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    Fermi Explores Supernova Remnants
    2010.02.13
    Fermi's Large Area Telescope (LAT) resolved gamma rays with energies a billion times greater than that of visible light from supernova remnants of different ages and in different environments. W51C, W44 and IC 443 are middle-aged remnants between 4,000 and 30,000 years old. The youngest remnant, Cassiopeia A, is only 330 years old and appears to the LAT as a point source. The images bring astronomers a step closer to understanding the source of some of the universe's most energetic particles — cosmic rays. The emissions are likely the result of accelerated protons interacting with nearby gas clouds, but other possibilities have not been eliminated. Astrophysicists believe that supernova remnants are the galaxy's best candidate sites for cosmic-ray acceleration. These observations provide further validation to the notion that supernova remnants act as enormous accelerators for cosmic particles.
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    How to make a gamma ray
    2010.11.09
    A series of animations showing how gamma rays can be created through various particle interactions.
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    NASA's Fermi Satellite Kicks Off a Blazar Bonanza
    2015.12.15
    A long time ago in a galaxy half the universe away, a flood of high-energy gamma rays began its journey to Earth. When they arrived in April, NASA's Fermi Gamma-ray Space Telescope caught the outburst, which helped two ground-based gamma-ray observatories detect some of the highest-energy light ever seen from a galaxy so distant. Astronomers had assumed that light at different energies came from regions at different distances from the black hole. Gamma rays, the highest-energy form of light, were thought to be produced closest in. But observations across the spectrum suggest that light at all wavelengths came from a single region located far away roughly five light-years from the black hole, which is greater than the distance between our sun and the nearest star. The gamma rays came from a galaxy known as PKS 1441+25, a type of active galaxy called a blazar. Located toward the constellation Boötes, the galaxy is so far away its light takes 7.6 billion years to reach us. At its heart lies a monster black hole with a mass estimated at 70 million times the sun's and a surrounding disk of hot gas and dust. If placed at the center of our solar system, the black hole's event horizon -- the point beyond which nothing can escape -- would extend almost to the orbit of Mars. As material in the disk falls toward the black hole, some of it forms dual particle jets that blast out of the disk in opposite directions at nearly the speed of light. Blazars are so bright in gamma rays because one jet points almost directly toward us, giving astronomers a view straight into the black hole's dynamic and poorly understood realm. In April, PKS 1441+25 underwent a major eruption. Luigi Pacciani at the Italian National Institute for Astrophysics in Rome was leading a project to catch blazar flares in their earliest stages in collaboration with the Major Atmospheric Gamma-ray Imaging Cerenkov experiment (MAGIC), located on La Palma in the Canary Islands. Using public Fermi data, Pacciani discovered the outburst and immediately alerted the astronomical community. Fermi's Large Area Telescope revealed gamma rays up to 33 billion electron volts (GeV), reaching into the highest-energy part of the instrument's detection range. For comparison, visible light has energies between about 2 and 3 electron volts. Following up on the Fermi alert, the MAGIC team turned to the blazar and detected gamma rays with energies ranging from 40 to 250 GeV. Because this galaxy is so far away, we didn't have a strong expectation of detecting gamma rays with energies this high. That’s because distance matters for very high-energy gamma rays -- they convert into particles when they collide with lower-energy light. The visible and ultraviolet light from stars shining throughout the history of the universe forms a remnant glow called the extragalactic background light (EBL). For gamma rays, this is a cosmic gauntlet they must pass through to be detected at Earth. When a gamma ray encounters starlight, it transforms into an electron and a positron and is lost to astronomers. The farther away the blazar is, the less likely its highest-energy gamma rays will survive to be detected. Following the MAGIC discovery, VERITAS also detected gamma rays with energies approaching 200 GeV. PKS 1441+25 is one of only two such distant sources for which gamma rays with energies above 100 GeV have been observed. Its dramatic flare provides a powerful glimpse into the intensity of the EBL from near-infrared to near-ultraviolet wavelengths and suggests that galaxy surveys have identified most of the sources responsible for it.
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    NASA's Fermi Preps to Narrow Down Gravitational Wave Sources
    2016.04.18
    On Sept. 14, waves of energy traveling for more than a billion years gently rattled space-time in the vicinity of Earth. The disturbance, produced by a pair of merging black holes, was captured by the Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Hanford, Washington, and Livingston, Louisiana. This event marked the first-ever detection of gravitational waves and opens a new scientific window on how the universe works. Less than half a second later, the Gamma-ray Burst Monitor (GBM) on NASA's Fermi Gamma-ray Space Telescope picked up a brief, weak burst of high-energy light consistent with the same part of the sky. Analysis of this burst suggests just a 0.2-percent chance of simply being random coincidence. Gamma-rays arising from a black hole merger would be a landmark finding because black holes are expected to merge “cleanly,” without producing any sort of light. Detecting light from a gravitational wave source will enable a much deeper understanding of the event. With its wide energy range and large field of view, the GBM is the premier instrument for detecting light from short gamma-ray bursts (GRBs), which last less than two seconds. They are widely thought to occur when orbiting compact objects, like neutron stars and black holes, spiral inward and crash together. These same systems also are suspected to be prime producers of gravitational waves. Currently, gravitational wave observatories possess relatively blurry vision. For the September event, dubbed GW150914 after the date, LIGO scientists could only trace the source to an arc of sky spanning an area of about 600 square degrees, comparable to the angular area on Earth occupied by the United States. Assuming the GBM burst is connected to this event, the GBM localization and Fermi's view of Earth combine to reduce the LIGO search area by about two-thirds, to 200 square degrees. With a burst better placed for the GBM’s detectors, or one bright enough to be seen by Fermi’s Large Area Telescope, even greater improvements are possible. Black hole mergers were not expected to emit significant X-ray or gamma-ray signals because orbiting gas is needed to generate light. Theorists expected any gas around binary black holes would have been swept up long before their final plunge. For this reason, some astronomers view the GBM burst as most likely a coincidence and unrelated to GW150914. Others have developed alternative scenarios where merging black holes could create observable gamma-ray emission. It will take further detections to clarify what really happens when black holes collide.
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    Ten Years of High-Energy Gamma-ray Bursts
    2019.06.13
    For a decade, NASA’s Fermi Gamma-ray Space Telescope has scanned the sky for gamma-ray bursts (GRBs), the universe’s most luminous explosions. A new catalog of the highest-energy blasts provides scientists with fresh insights into how they work. GRBs emit gamma rays, the highest-energy form of light. Most GRBs occurs when some types of massive stars run out of fuel and collapse to create new black holes. Others happen when two neutron stars, superdense remnants of stellar explosions, merge. Both kinds of cataclysmic events create jets of particles that move near the speed of light. The gamma rays are produced in collisions of fast-moving material inside the jets and when the jets interact with the environment around the star. Astronomers can distinguish the two GRB classes by the duration of their lower-energy gamma rays. Short bursts from neutron star mergers last less than 2 seconds, while long bursts typically continue for a minute or more. The new catalog, which includes 17 short and 169 long bursts, describes 186 events seen by Fermi’s Large Area Telescope (LAT) over the last 10 years. The LAT sees about one-fifth of the sky at any time and records gamma rays with energies above 30 million electron volts (MeV) — millions of times the energy of visible light. Fermi’s other instrument, the Gamma-ray Burst Monitor (GBM), sees the entire sky that isn’t blocked by Earth and detects lower-energy emission. All told, the GBM has detected more than 2,300 GRBs so far.
    GRB 130427A set the record for the highest-energy individual gamma ray detected by the LAT instrument. It also holds the record for the most gamma rays — 17 — with energies above 10 billion electron volts. The animation below illustrates the formation of a long GRB and its gamma-ray jets.
    GRB 090510 helped test Einstein’s theory that all forms of light travel through the vacuum of space at the same speed. Learn more about the event in the video below, starting at 0:59.
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    Fermi's Gamma-ray Burst Monitor
    2018.08.17
    The Gamma-ray Burst Monitor (GBM) is one of the instruments aboard the Fermi Gamma-ray Space Telescope. The GBM studies gamma-ray bursts, the most powerful explosions in the universe, as well as other flashes of gamma rays. Gamma-ray bursts are created when massive stars collapse into black holes or when two superdense stars merge, also producing a black hole. The GBM sees these bursts across the entire sky, and scientists are using its observations to learn more about the universe.

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    Watch this video on the NASA Goddard YouTube channel.

    Complete transcript available.

Cosmic Rays

  •
    Fermi Sees the Moon in Gamma Rays
    2019.08.15
    If our eyes could see high-energy radiation called gamma rays, the Moon would appear brighter than the Sun! That’s how NASA’s Fermi Gamma-ray Space Telescope has seen our neighbor in space for the past decade. Gamma-ray observations are not sensitive enough to clearly see the shape of the Moon’s disk or any surface features. Instead, Fermi’s Large Area Telescope (LAT) detects a prominent glow centered on the Moon’s position in the sky. Scientists have been analyzing the Moon’s gamma-ray glow as a way of better understanding another type of radiation from space: fast-moving particles called cosmic rays. Cosmic rays are mostly protons accelerated by some of the most energetic phenomena in the universe. Because the particles are electrically charged, they’re strongly affected by magnetic fields, which the Moon lacks. As a result, even low-energy cosmic rays can reach the surface, turning the Moon into a handy space-based particle detector. When cosmic rays strike, they interact with the powdery surface of the Moon, called the regolith, to produce gamma-ray emission. The Moon absorbs most of these gamma rays, but some of them escape. Mazziotta and Loparco analyzed Fermi LAT lunar observations to show how the view has improved during the mission. They rounded up data for gamma rays with energies above 31 million electron volts — 10 million times greater than the energy of visible light — and organized them over time, showing how longer exposures improve the view. Seen at these energies, the Moon would never go through its monthly cycle of phases and would always look full.
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    NASA's Fermi Satellite Kicks Off a Blazar Bonanza
    2015.12.15
    A long time ago in a galaxy half the universe away, a flood of high-energy gamma rays began its journey to Earth. When they arrived in April, NASA's Fermi Gamma-ray Space Telescope caught the outburst, which helped two ground-based gamma-ray observatories detect some of the highest-energy light ever seen from a galaxy so distant. Astronomers had assumed that light at different energies came from regions at different distances from the black hole. Gamma rays, the highest-energy form of light, were thought to be produced closest in. But observations across the spectrum suggest that light at all wavelengths came from a single region located far away roughly five light-years from the black hole, which is greater than the distance between our sun and the nearest star. The gamma rays came from a galaxy known as PKS 1441+25, a type of active galaxy called a blazar. Located toward the constellation Boötes, the galaxy is so far away its light takes 7.6 billion years to reach us. At its heart lies a monster black hole with a mass estimated at 70 million times the sun's and a surrounding disk of hot gas and dust. If placed at the center of our solar system, the black hole's event horizon -- the point beyond which nothing can escape -- would extend almost to the orbit of Mars. As material in the disk falls toward the black hole, some of it forms dual particle jets that blast out of the disk in opposite directions at nearly the speed of light. Blazars are so bright in gamma rays because one jet points almost directly toward us, giving astronomers a view straight into the black hole's dynamic and poorly understood realm. In April, PKS 1441+25 underwent a major eruption. Luigi Pacciani at the Italian National Institute for Astrophysics in Rome was leading a project to catch blazar flares in their earliest stages in collaboration with the Major Atmospheric Gamma-ray Imaging Cerenkov experiment (MAGIC), located on La Palma in the Canary Islands. Using public Fermi data, Pacciani discovered the outburst and immediately alerted the astronomical community. Fermi's Large Area Telescope revealed gamma rays up to 33 billion electron volts (GeV), reaching into the highest-energy part of the instrument's detection range. For comparison, visible light has energies between about 2 and 3 electron volts. Following up on the Fermi alert, the MAGIC team turned to the blazar and detected gamma rays with energies ranging from 40 to 250 GeV. Because this galaxy is so far away, we didn't have a strong expectation of detecting gamma rays with energies this high. That’s because distance matters for very high-energy gamma rays -- they convert into particles when they collide with lower-energy light. The visible and ultraviolet light from stars shining throughout the history of the universe forms a remnant glow called the extragalactic background light (EBL). For gamma rays, this is a cosmic gauntlet they must pass through to be detected at Earth. When a gamma ray encounters starlight, it transforms into an electron and a positron and is lost to astronomers. The farther away the blazar is, the less likely its highest-energy gamma rays will survive to be detected. Following the MAGIC discovery, VERITAS also detected gamma rays with energies approaching 200 GeV. PKS 1441+25 is one of only two such distant sources for which gamma rays with energies above 100 GeV have been observed. Its dramatic flare provides a powerful glimpse into the intensity of the EBL from near-infrared to near-ultraviolet wavelengths and suggests that galaxy surveys have identified most of the sources responsible for it.
  •
    Superstar Eta Carinae Shoots Cosmic Rays
    2018.07.03
    A new study using data from NASA’s NuSTAR space telescope suggests that the most luminous and massive stellar system within 10,000 light-years, Eta Carinae, is accelerating particles to high energies -- some of which may reach Earth as cosmic rays. Cosmic rays with energies greater than 1 billion electron volts (eV) come to us from beyond our solar system. But because these particles -- electrons, protons and atomic nuclei -- all carry an electrical charge, they veer off course whenever they encounter magnetic fields. This scrambles their paths and masks their origins. Eta Carinae, located about 7,500 light-years away in the southern constellation of Carina, contains a pair of massive stars whose eccentric orbits bring them unusually close every 5.5 years. The stars contain 90 and 30 times the mass of our Sun. Both stars drive powerful outflows called stellar winds, which emit low-energy X-rays where they collide. NASA’s Fermi Gamma-ray Space Telescope observes gamma rays -- light packing far more energy than X-rays -- from a source in the direction of Eta Carinae. But Fermi’s vision isn’t as sharp as X-ray telescopes, so astronomers couldn’t confirm the connection. To bridge this gap, astronomers turned to NASA's NuSTAR observatory. Launched in 2012, NuSTAR can focus X-rays of much greater energy than any previous telescope. The team examined NuSTAR observations acquired between March 2014 and June 2016, along with lower-energy X-ray observations from the European Space Agency’s XMM-Newton satellite over the same period. NuSTAR detects a source emitting X-rays above 30,000 eV, some three times higher than can be explained by shock waves in the colliding winds. For comparison, the energy of visible light ranges from about 2 to 3 eV. The researchers say both the X-ray emission seen by NuSTAR and the gamma-ray emission seen by Fermi is best explained by electrons accelerated in shock waves where the winds collide. The X-rays detected by NuSTAR and the gamma rays detected by Fermi arise from starlight given a huge energy boost by interactions with these electrons. Some of the superfast electrons, as well as other accelerated particles, must escape the system and perhaps some eventually wander to Earth, where they may be detected as cosmic rays.
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    SuperTIGER Ready to Fly Again in Study of Heavy Cosmic Rays
    2017.12.06
    Due to uncooperative weather in Antarctica, SuperTIGER was unable to launch during the 2017-18 balloon season. The team returned to the ice in November 2018, preparing for their first launch opportunity of the 2018-19 season! Scientists in Antarctica are preparing to loft a NASA balloon-borne instrument to collect information on cosmic rays, high-energy particles from beyond the solar system that enter Earth's atmosphere every moment of every day. The instrument, called the Super Trans-Iron Galactic Element Recorder (SuperTIGER), is designed to study rare heavy nuclei, which hold clues about where and how cosmic rays attain speeds up to nearly the speed of light. The most common cosmic ray particles are protons (hydrogen nuclei), making up roughly 90 percent, followed by helium nuclei (8 percent) and electrons (1 percent). The remainder contains the nuclei of other elements, with dwindling numbers of heavy nuclei as their masses rise. With SuperTIGER, researchers are looking for the rarest of the rare -- so-called ultra-heavy cosmic ray nuclei beyond iron, from cobalt to barium. These elements are formed in some of the most extreme environments in the cosmos -- outflows from massive stars, supernova explosions, and mergers of neutron stars. Learning more about the distribution of the heavy cosmic rays will help astronomers further narrow down the places and processes forming them.
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    Fermi Proves Supernova Remnants Produce Cosmic Rays
    2013.02.14
    A new study using observations from NASA's Fermi Gamma-ray Space Telescope reveals the first clear-cut evidence that the expanding debris of exploded stars produces some of the fastest-moving matter in the universe. This discovery is a major step toward meeting one of Fermi's primary mission goals.

    Cosmic rays are subatomic particles that move through space at nearly the speed of light. About 90 percent of them are protons, with the remainder consisting of electrons and atomic nuclei. In their journey across the galaxy, the electrically charged particles become deflected by magnetic fields. This scrambles their paths and makes it impossible to trace their origins directly.

    Through a variety of mechanisms, these speedy particles can lead to the emission of gamma rays, the most powerful form of light and a signal that travels to us directly from its sources.

    Two supernova remnants, known as IC 443 and W44, are expanding into cold, dense clouds of interstellar gas. This material emits gamma rays when struck by high-speed particles escaping the remnants.

    Scientists have been unable to ascertain which particle is responsible for this emission because cosmic-ray protons and electrons give rise to gamma rays with similar energies. Now, after analyzing four years of data, Fermi scientists see a gamma-ray feature from both remnants that, like a fingerprint, proves the culprits are protons.

    When cosmic-ray protons smash into normal protons, they produce a short-lived particle called a neutral pion. The pion quickly decays into a pair of gamma rays. This emission falls within a specific band of energies associated with the rest mass of the neutral pion, and it declines steeply toward lower energies.

    Detecting this low-end cutoff is clear proof that the gamma rays arise from decaying pions formed by protons accelerated within the supernova remnants.

    In 1949, the Fermi telescope's namesake, physicist Enrico Fermi, suggested that the highest-energy cosmic rays were accelerated in the magnetic fields of interstellar gas clouds. In the decades that followed, astronomers showed that supernova remnants were the galaxy's best candidate sites for this process.?

    A charged particle trapped in a supernova remnant's magnetic field moves randomly throughout it and occasionally crosses through the explosion's leading shock wave. Each round trip through the shock ramps up the particle's speed by about 1 percent. After many crossings, the particle obtains enough energy to break free and escapes into the galaxy as a newborn cosmic ray.

    The Fermi discovery builds on a strong hint of neutral pion decay in W44 observed by the Italian Space Agency's AGILE gamma-ray observatory and published in late 2011.

    Watch this video on YouTube.

  •
    Fermi Explores Supernova Remnants
    2010.02.13
    Fermi's Large Area Telescope (LAT) resolved gamma rays with energies a billion times greater than that of visible light from supernova remnants of different ages and in different environments. W51C, W44 and IC 443 are middle-aged remnants between 4,000 and 30,000 years old. The youngest remnant, Cassiopeia A, is only 330 years old and appears to the LAT as a point source. The images bring astronomers a step closer to understanding the source of some of the universe's most energetic particles — cosmic rays. The emissions are likely the result of accelerated protons interacting with nearby gas clouds, but other possibilities have not been eliminated. Astrophysicists believe that supernova remnants are the galaxy's best candidate sites for cosmic-ray acceleration. These observations provide further validation to the notion that supernova remnants act as enormous accelerators for cosmic particles.
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    Cosmic Rays and the Heliopause
    2010.10.01
    This animation shows how variations in the size of the heliosphere affect how many cosmic rays reach Earth. As the heliosphere expands, it blocks more cosmic rays, and as it contracts, more cosmic rays get through and can affect astronauts and satellites.
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    How Cosmic-ray Protons Make Gamma rays
    2010.02.13
    In the simplest and most common interaction, a cosmic-ray proton strikes another proton. The protons survive the collision, but their interaction creates an unstable particle — a pion — with only 14 percent the mass of a proton. In 10 millionths of a billionth of a second, the pion decays into a pair of gamma-ray photons. More complex scenarios occur when cosmic-ray protons strike nuclei containing greater numbers of particles.
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    How to make a gamma ray
    2010.11.09
    A series of animations showing how gamma rays can be created through various particle interactions.

Neutrinos

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    NASA's Fermi Links Cosmic Neutrino to Monster Black Hole
    2018.07.12
    For the first time ever, scientists using NASA’s Fermi Gamma-ray Space Telescope have found the source of a high-energy neutrino from outside our galaxy. This neutrino travelled 3.7 billion years at nearly light speed before being detected on Earth -- farther than any other neutrino we know the origin of. High-energy neutrinos are hard-to-catch particles that scientists think are created by the most powerful events in the cosmos, like galaxy mergers and material falling onto supermassive black holes. They travel a whisker shy of the speed of light and rarely interact with other matter, so they can travel unimpeded across billions of light-years. On Sept. 22, 2017, the IceCube Neutrino Observatory at the South Pole detected signs of a neutrino striking the Antarctic ice with an energy of about 300 trillion electron volts -- more than 45 times the energy achievable in the most powerful particle accelerator on Earth. This high energy strongly suggested that the neutrino had to be from beyond our solar system. Backtracking the path through IceCube indicated where in the sky the neutrino came from, and automated alerts notified astronomers around the globe to search this region for flares or outbursts that could be associated with the event. Data from Fermi’s Large Area Telescope revealed enhanced gamma-ray emission from a well-known active galaxy at the time the neutrino arrived. This active galaxy is a type called a blazar, where a supermassive black hole with millions to billions of times the Sun’s mass that blasts particle jets outward in opposite directions at nearly the speed of light. Blazars are especially bright and active because one of these jets happens to point almost directly toward Earth. Fermi showed that at the time of the neutrino detection, the blazar TXS 0506+056 was the most active it had been in a decade. The discovery is a giant leap forward in a growing field called multimessenger astronomy, where new cosmic signals like neutrinos and gravitational waves are definitively linked to sources that emit light.
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    Blazar Animations
    2018.07.12
    This animation shows the central supermassive black hole of a blazar. The black hole is surrounded by a bright accretion disk and a darker torus of gas and dust. A bright jet of particles emerges from above and below the black hole. Collisions within the jet produce high-energy photons such as gamma rays. A flare from the blazar results in an additional burst of gamma rays and neutrinos.
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    Fermi Helps Link a Cosmic Neutrino to a Blazar Outburst
    2016.04.28
    Nearly 10 billion years ago, the black hole at the center of a distant galaxy produced a powerful outburst, and light from this blast began arriving at Earth in 2012. Astronomers using data from NASA's Fermi Gamma-ray Space Telescope and other space- and ground-based observatories have shown that a record-breaking neutrino seen around the same time likely was born in the same event. Neutrinos are the fastest, lightest, most unsociable and least understood fundamental particles. The study provides the first plausible association between a single extragalactic object and a high-energy cosmic neutrino. Although neutrinos far outnumber all the atoms in the universe, they rarely interact with matter. While this property makes them hard to detect, it lets neutrinos make a fast exit from places where light cannot easily escape -- such as the core of a collapsing star -- and zip across the universe almost completely unimpeded. Neutrinos can provide information about processes and environments that simply aren't available through a study of light alone. The IceCube Neutrino Observatory, built into a cubic kilometer of clear glacial ice at the South Pole, detects neutrinos when they interact with atoms in the ice. Some of the most extreme particles detected by IceCube receive nicknames based on characters on the children's TV series "Sesame Street." On Dec. 4, 2012, IceCube detected an event known as Big Bird, a neutrino with an energy exceeding 2 quadrillion electron volts (PeV), the highest-energy neutrino ever detected at the time. But the best IceCube position only narrowed the source to a patch of the southern sky about 32 degrees across, equivalent to the apparent size of 64 full moons. In the summer of 2012, Fermi's Large Area Telescope (LAT) witnessed the onset of a dramatic brightening of PKS B1424-418, an active galaxy classified as a gamma-ray blazar. An active galaxy is an otherwise typical galaxy with a compact and unusually bright core; this excess luminosity is produced by matter falling toward a supermassive black hole weighing millions of times the mass of our sun. As it approaches the black hole, some of the material becomes channeled into particle jets moving outward in opposite directions at nearly the speed of light. In blazars, one of these jets happens to point almost directly toward Earth. During the year-long outburst, PKS B1424-418 shone between 15 and 30 times brighter in gamma rays than its average before the eruption. The blazar is located within the Big Bird source region, but so are many other active galaxies detected by Fermi. Was it the culprit? Astronomers investigating the link turned to the TANAMI project, which since 2007 has routinely monitored dozens of active galaxies in the southern sky. The program includes regular radio observations using the Australian Long Baseline Array (LBA) and associated telescopes in Chile, South Africa, New Zealand and Antarctica. When networked together, they operate as a single radio telescope more than 6,000 miles across and provide a unique high-resolution look into the jets of active galaxies. Three radio observations of PKS B1424-418 between 2011 and 2013 cover the period of the Fermi outburst. They reveal that the core of the galaxy's jet had brightened by about four times. No other galaxy observed by TANAMI over the life of the program has exhibited such a dramatic change. The team suggests the PKS B1424-418 outburst and Big Bird are connected, calculating only a 5-percent probability the two events occurred by chance alone. Using data from Fermi, NASA’s Swift and WISE satellites, the LBA and other facilities, the researchers determined how the energy of the eruption was distributed across the electromagnetic spectrum and showed that it was sufficiently powerful to produce a neutrino at PeV energies.
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    X-ray Telescopes Find Black Hole May Be a Neutrino Factory
    2015.01.15
    The supermassive black hole at the center of the Milky Way, seen in this image from NASA's Chandra X-ray Observatory, may be producing mysterious particles called neutrinos, as described in our latest press release. Neutrinos are tiny particles that have virtually no mass and carry no electric charge. Unlike light or charged particles, neutrinos can emerge from deep within their sources and travel across the Universe without being absorbed by intervening matter or, in the case of charged particles, deflected by magnetic fields. Using three NASA X-ray telescopes, Chandra, Swift, and NuSTAR, scientists have found evidence for one such cosmic source for high-energy neutrinos: the 4-million-solar-mass black hole at the center of our Galaxy called Sagittarius A* (Sgr A*, for short). After comparing the arrival of high-energy neutrinos at the underground facility in Antarctica, called IceCube, with outbursts from Sgr A*, a team of researchers found a correlation. This Chandra image shows the region around Sgr A* in low, medium, and high-energy X-rays that have been colored red, green, and blue respectively. Sgr A* is located within the white area in the center of the image. The blue and orange plumes around that area may be the remains of outbursts from Sgr A* that occurred millions of years ago. The flares that are possibly associated with the IceCube neutrinos involve just the Sgr A* X-ray source.

Gravitational Waves

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    Doomed Neutron Stars Create Blast of Light and Gravitational Waves
    2017.10.16
    For the first time, NASA scientists have detected light tied to a gravitational-wave event, thanks to two merging neutron stars in the galaxy NGC 4993, located about 130 million light-years from Earth in the constellation Hydra. Shortly after 8:41 a.m. EDT on Aug. 17, NASA's Fermi Gamma-ray Space Telescope picked up a pulse of high-energy light from a powerful explosion, which was immediately reported to astronomers around the globe as a short gamma-ray burst. The scientists at the National Science Foundation’s Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational waves dubbed GW170817 from a pair of smashing stars tied to the gamma-ray burst, encouraging astronomers to look for the aftermath of the explosion. Shortly thereafter, the burst was detected as part of a follow-up analysis by ESA’s (European Space Agency’s) INTEGRAL satellite. NASA's Swift, Hubble, Chandra and Spitzer missions, along with dozens of ground-based observatories, including the NASA-funded Pan-STARRS survey, later captured the fading glow of the blast's expanding debris. Neutron stars are the crushed, leftover cores of massive stars that previously exploded as supernovas long ago. The merging stars likely had masses between 10 and 60 percent greater than that of our Sun, but they were no wider than Washington, D.C. The pair whirled around each other hundreds of times a second, producing gravitational waves at the same frequency. As they drew closer and orbited faster, the stars eventually broke apart and merged, producing both a gamma-ray burst and a rarely seen flare-up called a "kilonova." Neutron star mergers produce a wide variety of light because the objects form a maelstrom of hot debris when they collide. Merging black holes -- the types of events LIGO and its European counterpart, Virgo, have previously seen -- very likely consume any matter around them long before they crash, so we don't expect the same kind of light show. Within hours of the initial Fermi detection, LIGO and the Virgo detector at the European Gravitational Observatory near Pisa, Italy, greatly refined the event's position in the sky with additional analysis of gravitational wave data. Ground-based observatories then quickly located a new optical and infrared source -- the kilonova -- in NGC 4993. To Fermi, this appeared to be a typical short gamma-ray burst, but it occurred less than one-tenth as far away as any other short burst with a known distance, making it among the faintest known. Astronomers are still trying to figure out why this burst is so odd, and how this event relates to the more luminous gamma-ray bursts seen at much greater distances. NASA’s Swift, Hubble and Spitzer missions followed the evolution of the kilonova to better understand the composition of this slower-moving material, while Chandra searched for X-rays associated with the remains of the ultra-fast jet.
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    Astrophysics Live Shot 10.17.2017
    2017.10.13
    An exciting discovery out of NASA’s Goddard Space Flight Center! The bling in your ring is a product of the most violent kind of explosion in the universe.

    Suggested Anchor Intro:
    Yesterday scientists announced another giant discovery in the physics world. This time, it involves the most powerful explosion in the universe, head-banging stars and a cosmic gold rush. We have NASA scientist *NAME* here to give us a bite-sized astrophysics lesson.

    While observing a galaxy 130 million light-years away, NASA scientists became the first to see a gamma-ray burst caused by two neutron stars smashing into each other. Join some of these brilliant minds from 6:00-11:30 a.m. ET on Tuesday, Oct. 17, for a bite-sized astrophysics lesson about an exciting discovery: many precious metals on Earth are remnants of these stellar collisions. This particular explosion produced 500 times the mass of Earth in platinum and 200 times the mass of Earth in gold.

    Gamma-ray bursts are the most powerful explosions in the cosmos. Most occur when a massive star collapses under its own weight as it nears the end of its life. For decades scientists have suspected these bursts might also come from something else: collisions between neutron stars, the smallest and densest stars known to exist — they were right. Black holes merge darkly, but neutron stars do so with a splash. Matter is packed so tightly in neutron stars that a sugar cube-sized amount of material would weigh as much as Mount Everest. So, as it turns out, a neutron star merger can fuel the creation of precious metals and scatter them across the universe — precisely how gold, platinum and dozens of other elements arrived at Earth.

    We now know that a neutron star merger is powerful enough to cause ripples in space-time, just as a rock thrown into a pond creates ripples in the water. The discovery of these gravitational waves earned three physicists a 2017 Nobel Prize. This neutron star collision marks the first time scientists have been able to pinpoint exactly where gravitational waves originated. This discovery brings remarkable new insights into the physics behind the most powerful explosions in the universe — and a reminder that we're surrounded by the stuff of stars.

    Suggested Questions:
    1. Walk us through this incredible discovery. What did you see?
    2. So, the gold in my ring is stardust? How did these heavy metals get to Earth?
    3. This isn't the first time you've seen an explosion like this. Why is this one so special?
    4. The science community is pretty excited about gravitational waves. What are they?
    5. Where can we learn more?

    Location: NASA's Goddard Space Flight Center/Greenbelt, Maryland

    Scientists:
    Dr. Brad Cenko / NASA Astrophysicist, Goddard Space Flight Center
    Dr. Paul Hertz / Director, Astrophysics Science Division, NASA Headquarters
    Dr. Julie McEnery / NASA Astrophysicist, Goddard Space Flight Center

    To book a window contact: 
 Micheala Sosby / micheala.m.sosby@nasa.gov / 301-286-8199

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    Listening to the Universe with Gravitational Waves
    2015.01.15
    Dr. Ira Thorpe's AAS presentation from 2015
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    NASA's Fermi Preps to Narrow Down Gravitational Wave Sources
    2016.04.18
    On Sept. 14, waves of energy traveling for more than a billion years gently rattled space-time in the vicinity of Earth. The disturbance, produced by a pair of merging black holes, was captured by the Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Hanford, Washington, and Livingston, Louisiana. This event marked the first-ever detection of gravitational waves and opens a new scientific window on how the universe works. Less than half a second later, the Gamma-ray Burst Monitor (GBM) on NASA's Fermi Gamma-ray Space Telescope picked up a brief, weak burst of high-energy light consistent with the same part of the sky. Analysis of this burst suggests just a 0.2-percent chance of simply being random coincidence. Gamma-rays arising from a black hole merger would be a landmark finding because black holes are expected to merge “cleanly,” without producing any sort of light. Detecting light from a gravitational wave source will enable a much deeper understanding of the event. With its wide energy range and large field of view, the GBM is the premier instrument for detecting light from short gamma-ray bursts (GRBs), which last less than two seconds. They are widely thought to occur when orbiting compact objects, like neutron stars and black holes, spiral inward and crash together. These same systems also are suspected to be prime producers of gravitational waves. Currently, gravitational wave observatories possess relatively blurry vision. For the September event, dubbed GW150914 after the date, LIGO scientists could only trace the source to an arc of sky spanning an area of about 600 square degrees, comparable to the angular area on Earth occupied by the United States. Assuming the GBM burst is connected to this event, the GBM localization and Fermi's view of Earth combine to reduce the LIGO search area by about two-thirds, to 200 square degrees. With a burst better placed for the GBM’s detectors, or one bright enough to be seen by Fermi’s Large Area Telescope, even greater improvements are possible. Black hole mergers were not expected to emit significant X-ray or gamma-ray signals because orbiting gas is needed to generate light. Theorists expected any gas around binary black holes would have been swept up long before their final plunge. For this reason, some astronomers view the GBM burst as most likely a coincidence and unrelated to GW150914. Others have developed alternative scenarios where merging black holes could create observable gamma-ray emission. It will take further detections to clarify what really happens when black holes collide.
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    Gravitational Waves from Black Holes
    2007.07.03
    A gravitational wave is a theoretical fluctuation in the curvature of spacetime caused by the movement of incredibly massive objects. In this animation, two massive black holes orbit each other, creating gravitational waves.
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    Simulations Uncover 'Flashy' Secrets of Merging Black Holes
    2012.09.27
    According to Einstein, whenever massive objects interact, they produce gravitational waves — distortions in the very fabric of space and time — that ripple outward across the universe at the speed of light. While astronomers have found indirect evidence of these disturbances, the waves have so far eluded direct detection. Ground-based observatories designed to find them are on the verge of achieving greater sensitivities, and many scientists think that this discovery is just a few years away.

    Catching gravitational waves from some of the strongest sources — colliding black holes with millions of times the sun's mass — will take a little longer. These waves undulate so slowly that they won't be detectable by ground-based facilities. Instead, scientists will need much larger space-based instruments, such as the proposed Laser Interferometer Space Antenna, which was endorsed as a high-priority future project by the astronomical community.

    A team that includes astrophysicists at NASA's Goddard Space Flight Center in Greenbelt, Md., is looking forward to that day by using computational models to explore the mergers of supersized black holes. Their most recent work investigates what kind of "flash" might be seen by telescopes when astronomers ultimately find gravitational signals from such an event.

    To explore the problem, a team led by Bruno Giacomazzo at the University of Colorado, Boulder, and including Baker developed computer simulations that for the first time show what happens in the magnetized gas (also called a plasma) in the last stages of a black hole merger.

    In the turbulent environment near the merging black holes, the magnetic field intensifies as it becomes twisted and compressed. The team suggests that running the simulation for additional orbits would result in even greater amplification.

    The most interesting outcome of the magnetic simulation is the development of a funnel-like structure — a cleared-out zone that extends up out of the accretion disk near the merged black hole.

    The most important aspect of the study is the brightness of the merger's flash. The team finds that the magnetic model produces beamed emission that is some 10,000 times brighter than those seen in previous studies, which took the simplifying step of ignoring plasma effects in the merging disks.

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    LISA Pathfinder Spaceflight Experiment a Rousing Success
    2016.06.07
    LISA Pathfinder, a mission led by the European Space Agency (ESA) with contributions from NASA, has successfully tested a key technology needed to build a space-based observatory for detecting gravitational waves. These tiny ripples in the fabric of space, predicted by Albert Einstein a century ago, were first seen last year by the ground-based Laser Interferometer Gravitational-Wave Observatory (LIGO). Seismic, thermal, and other noise sources limit LIGO to higher-frequency gravitational waves around 100 cycles per second (hertz). But finding signals from more exotic events, such as mergers of supermassive black holes in colliding galaxies, requires the ability to see frequencies at 1 hertz or less, a sensitivity level only possible from space. A space-based observatory would work by tracking test masses that move only under the influence of gravity. Each spacecraft would gently fly around its test masses without disturbing them, a process called drag-free flight. The primary goal of ESA's LISA Pathfinder mission is to test current technology by flying around an identical pair of 1.8-inch (46 millimeter) cubes made of a gold-platinum alloy, a material chosen for its high density and insensitivity to magnetic fields. Scientists say the results are nothing short of astonishing. Non-gravitational forces on the cubes were reduced to levels far below the project's original requirements and approach the level of control needed for a full-scale observatory. The test masses are housed in an experiment called the LISA Technology Package (LTP), which was built by a consortium of European national space agencies and ESA. The LTP uses a high-resolution laser interferometer to determine the positions of the test masses and relays the information to the spacecraft's Drag-Free and Attitude Control System, which then applies minute bursts from microthrusters. In this way, the spacecraft flies in formation with the cubes and isolates them from external forces. The results show that LISA Pathfinder reduced non-gravitational forces on the test masses to a level about 10,000 times smaller than drag-free control technologies used on previous science missions. LISA Pathfinder also carries a NASA experiment called the ST-7 Disturbance Reduction System. Managed by NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, the experiment combines novel "electrospray" thrusters with drag-free control software provided by Goddard on a dedicated computer. The experiment, which will use information on the position of the test masses provided by the LTP to determine how to move the spacecraft, is expected to begin science operations in early July. LISA Pathfinder was launched on Dec. 3, 2015, and began orbiting a point called Earth-sun L1, roughly 930,000 miles (1.5 million kilometers) from Earth in the sun's direction, in late January 2016. LISA stands for Laser Interferometer Space Antenna, a space-based gravitational wave observatory concept that has been studied in great detail by both NASA and ESA.