| [00:00:00.00] | [music throughout] Narrator: On August 21st, 2019, NASA’s NICER telescope |
| [00:00:05.00] | on the International Space Station observed its brightest X-ray burst to date. |
| [00:00:09.00] | The flare-up came from SAX J1808, a binary system |
| [00:00:13.00] | about 11,000 light-years away. Here, a pulsar— [ON-SCREEN TEXT: “SAX J1808.4-3658”] |
| [00:00:17.00] | a rapidly spinning neutron star—draws gas from its companion, |
| [00:00:21.00] | an object called a brown dwarf that is larger than a planet, but less massive than |
| [00:00:25.00] | a star. Hydrogen gas from the brown dwarf forms an accretion |
| [00:00:29.00] | disk around the pulsar. Every few years, the disk becomes unstable. |
| [00:00:33.00] | This sends a rush of gas toward the pulsar that makes it brighten |
| [00:00:37.00] | in X-rays. The pulsar’s superstrong magnetic field sweeps up |
| [00:00:41.00] | the gas and channels it to the object’s surface. |
| [00:00:45.00] | Hydrogen nuclei falling to the pulsar’s surface fuse together, producing energy [ON-SCREEN TEXT: “Infalling Hydrogen, Fusion” |
| [00:00:49.00] | and forming helium nuclei, which settle out below. This process [ON-SCREEN TEXT: “Infalling Hydrogen, Fusion, Helium Layer” |
| [00:00:53.00] | is similar to what happens inside our Sun. Then, when the conditions [ON-SCREEN TEXT: “Infalling Hydrogen, Fusion, Helium Layer” |
| [00:00:57.00] | are just right, the entire helium layer ignites in a brief, but intense |
| [00:01:01.00] | thermonuclear fireball. Astronomers call this a Type I [ON-SCREEN TEXT: “Type I X-ray Burst”] |
| [00:01:05.00] | X-ray burst. Here’s how it happened. [ON-SCREEN TEXT: “Type I X-ray Burst”] |
| [00:01:09.00] | The explosion first blows off the hydrogen layer, which expands and ultimately dissipates. Then, |
| [00:01:13.00] | the rising radiation builds to the point where it blows off the helium layer, |
| [00:01:17.00] | which overtakes the hydrogen shell. Some of the X-rays emitted in the blast |
| [00:01:21.00] | scatter off of the accretion disk. The fireball then |
| [00:01:25.00] | quickly cools, and the helium settles back onto the surface. |
| [00:01:29.00] | It was all over in 20 seconds, but NICER data clearly show [ON-SCREEN GRAPHICS/TEXT: Graph showing a light curve with two peaks. X-axis: “Time (seconds).” Y-axis: “X-ray counts (x 1,000).” Two highlighted areas are labeled “Hydrogen expansion” and “Helium expansion.” A third area is labeled “Unexplained rebrightening.”] |
| [00:01:33.00] | important details that haven’t been seen together in other bursts. [ON-SCREEN GRAPHICS/TEXT: Graph showing a light curve with two peaks. X-axis: “Time (seconds).” Y-axis: “X-ray counts (x 1,000).” Two highlighted areas are labeled “Hydrogen expansion” and “Helium expansion.” A third area is labeled “Unexplained rebrightening.”] |
| [00:01:37.00] | This will help scientists better understand the extreme physics of these eruptions |
| [00:01:41.00] | on accreting neutron stars. |
| [00:01:45.00] | [music] |