Large star forms black hole without going supernova
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by
Budgieye
moderator
He leads a team of astronomers who published their latest results in
the Monthly Notices of the Royal Astronomical Society. Among the
galaxies they've been watching is NGC 6946, a spiral galaxy 22 million
light-years away that is nicknamed the "Fireworks Galaxy" because
supernovae frequently happen there — indeed, SN 2017eaw, discovered on
May 14th, is shining near maximum brightness now. Starting in 2009,
one particular star, named N6946-BH1, began to brighten weakly. By
2015, it appeared to have winked out of existence.https://www.nasa.gov/feature/goddard/2017/collapsing-star-gives-birth-to-a-black-hole
This pair of visible-light and near-infrared Hubble Space Telescope
photos shows the giant star N6946-BH1 before and after it vanished out
of sight by imploding to form a black hole. The left image shows the
25 solar mass star as it looked in 2007. In 2009, the star shot up in
brightness to become over 1 million times more luminous than our sun
for several months. But then it seemed to vanish, as seen in the right
panel image from 2015. A small amount of infrared light has been
detected from where the star used to be. This radiation probably comes
from debris falling onto a black hole. The black hole is located 22
million light-years away in the spiral galaxy NGC 6946. Credits: NASA,
ESA, and C. Kochanek (OSU)
PanStARRS 2014
Fireworks Galaxy NGC 6946
Image Credit & Copyright: Adam Block, Mt. Lemmon SkyCenter, U. Arizonahttps://apod.nasa.gov/apod/ap110101.html
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I'm confused, since when can we image individual (non-supernova) stars located in other galaxies 22 million lightyears away? Or do they mean the debris falling onto 'a' black hole has nothing to do with the possibly imploded star?
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by
Ghost_Sheep_SWR
in response to Ghost_Sheep_SWR's comment.
Apparently we can. Difficult to fathom because of other galaxies might consist of billions or trillions of stars millions of lightyears away.
Here is an answer from someone on reddit who responded to the same sort of question;
It really depends on the scale you're talking about. For local galaxies - e.g. Andromeda, Fornax, etc. - it's possible possible to construct colour-magnitude diagrams using Hubble. For many of these galaxies it's also possible to obtained ground-based spectroscopy of individual, bright giant stars; this is feasible out to a distance of about ~1 Mpc. Outside of the local group this sort of work becomes difficult, though with Hubble it's possible to identify stars a few magnitudes down the red giant branch out as far as ~3-4 Mpc, and individual supergiant stars might be observable out to several tens of Mpc.
With proposed next-generation ground-based telescopes, such as TMT, GMT or the European E-ELT, it may be possible to carry out ground based spectroscopic work out on individual giant-branch stars out to the distance of the Virgo Cluster (~17 Mpc or so).
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Budgieye
moderator
Yes, we have to update our "everybody knows" occasionally. I knew some telescopes could resolve stars in Andromeda galaxy at 2 million light-years. I didn't know about 22 million light-years. I kept checking the article, because I was wondering if it was a foreground star.
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Yeah same here, also doesn't help they say 'a blackhole' instead of the black hole that resulted from THAT star's implosion. Kinda vague but scientific. And the reddit answer above talks about spectroscopy, not optical / visual imagery such as provided with the article to show the before and after image.
Still find it hard to believe at the moment, but I think that the biggest difference would be this star was really much brighter than the sun even before it started brightening. Hmpf will check the paper itself when I'm mentally up to such a barrage of scientific words, units and language 😉
EDIT btw the APOD page says 10 million ly not 22 mly, that's already ~ half the distance (..?) what's going on here? But 22 mly is current value.
Wiki on N6946-BH1 : Prior to the optical outburst the star was about 100,000 times as bright as the sun.
https://en.m.wikipedia.org/wiki/N6946-BH1
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Yup have to update once in a while. Phil Plait just tweeted about this article and answered my question:
Was wondering about a single star in a galaxy 22mly away being imaged. Only possible because it is such a bright type >right?
That made it easier, but fainter stars can be seen in that galaxy. Still have to be ~50X brighter than the Sun though.
Phil Plait / The Bad Astronomer
Article http://www.blastr.com/2017-5-31/astronomers-may-have-seen-star-collapse-directly-black-hole
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