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For the first time ever,
astronomers might have witnessed

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a star actually become a black
hole right before our eyes... or

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telescopes. In this visible
light image from the Hubble

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Space Telescope, we can see a
large star about 25 times the

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mass of our Sun around 22
million light years away in the

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galaxy NGC 6946. This was in
2007. But in a Hubble image from

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2015, looking with the same
filters at the same wavelengths,

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the star appears to be gone. One
possible explanation - the star

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died and became a black hole.
But it gets weirder. The most

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prevalent theory for how a black
hole forms is through a

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supernova - if a star is big
enough, at the end of its life

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it will eject its outer layers
at high velocity in a massive

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explosion while the inner core
collapses into a very tiny

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space, creating a gravity well
so great that light can’t

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escape. Literally, a black hole.
So did we see this star go

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supernova? No, not really. A
team of astronomers was

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monitoring this star with the
Large Binocular Telescope in

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Arizona and saw the star get
brighter in 2009, but not nearly

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as bright as a supernova. They
call it a failed supernova. The

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star does expel its outer-most
layer, but relatively gently and

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not in a big explosion. Ok, so
this star got brighter in

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visible light in 2009, and then
disappeared in visible light.

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How do we know it’s not just
hidden behind a cloud of dust or

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something? The team checked for
that; they looked at infrared

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observations from the Spitzer
Space Telescope, which would be

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able to see the heat of dust
warmed by the star. What we see

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with Spitzer is there is some
emission in the mid-infrared,

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but it’s fading and fainter than
what you’d expect to see with a

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hidden star. The team thinks
instead that this infrared light

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is from the heat of gas falling
back onto the newly formed black

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hole. To help confirm that this
star is now a black hole, the

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team plans to analyze
observations taken with the

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Chandra X-Ray Observatory, which
would be able to reveal X-rays

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being emitted by the gas falling
into the black hole. The team

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also wants to continue
monitoring the star’s location

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in visible light with Hubble,
in case the star is still
there and re-appears, and

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they’ll want to look at the
location with the upcoming James

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Webb Space Telescope to check if
there’s a surviving star hidden

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by cooler dust than can be
observed with Spitzer. So if

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this really is a black hole
birth, what does that mean for

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astronomy? First of all, this
would show that a star doesn’t

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need to go supernova to form a
black hole. Astronomers actually

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haven’t seen as many supernovas
occur with the largest stars as

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they would expect to see, and
they’ve been wondering why this

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is. Perhaps 10 to 30 percent of
massive stars don’t go supernova

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and are still able to simply
form a black hole. If future

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observations confirm this team’s
findings, this would be the

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first birth of a black hole ever
witnessed and the first failed

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supernova ever discovered, both
of which would usher in an

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exciting era of astronomy
research.

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www.nasa.gov/hubble 
@NASAHubble