Star Gives Birth to Possible Black Hole in Hubble and Spitzer Images

For the first time ever,
astronomers might have witnessed a star actually become a black
hole right before our eyes… or telescopes. In this visible
light image from the Hubble Space Telescope, we can see a
large star about 25 times the mass of our Sun around 22
million light years away in the galaxy NGC 6946. This was in
2007. But in a Hubble image from 2015, looking with the same
filters at the same wavelengths, the star appears to be gone. One
possible explanation – the star died and became a black hole.
But it gets weirder. The most prevalent theory for how a black
hole forms is through a supernova – if a star is big
enough, at the end of its life it will eject its outer layers
at high velocity in a massive explosion while the inner core
collapses into a very tiny space, creating a gravity well
so great that light can’t escape. Literally, a black hole.
So did we see this star go supernova? No, not really. A
team of astronomers was monitoring this star with the
Large Binocular Telescope in Arizona and saw the star get
brighter in 2009, but not nearly as bright as a supernova. They
call it a failed supernova. The star does expel its outer-most
layer, but relatively gently and not in a big explosion. Ok, so
this star got brighter in visible light in 2009, and then
disappeared in visible light. How do we know it’s not just
hidden behind a cloud of dust or something? The team checked for
that; they looked at infrared observations from the Spitzer
Space Telescope, which would be able to see the heat of dust
warmed by the star. What we see with Spitzer is there is some
emission in the mid-infrared, but it’s fading and fainter than
what you’d expect to see with a hidden star. The team thinks
instead that this infrared light is from the heat of gas falling
back onto the newly formed black hole. To help confirm that this
star is now a black hole, the team plans to analyze
observations taken with the Chandra X-Ray Observatory, which
would be able to reveal X-rays being emitted by the gas falling
into the black hole. The team also wants to continue
monitoring the star’s location in visible light with Hubble,
in case the star is still
there and re-appears, and they’ll want to look at the
location with the upcoming James Webb Space Telescope to check if
there’s a surviving star hidden by cooler dust than can be
observed with Spitzer. So if this really is a black hole
birth, what does that mean for astronomy? First of all, this
would show that a star doesn’t need to go supernova to form a
black hole. Astronomers actually haven’t seen as many supernovas
occur with the largest stars as they would expect to see, and
they’ve been wondering why this is. Perhaps 10 to 30 percent of
massive stars don’t go supernova and are still able to simply
form a black hole. If future observations confirm this team’s
findings, this would be the first birth of a black hole ever
witnessed and the first failed supernova ever discovered, both
of which would usher in an exciting era of astronomy

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