Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Dhruv on 29/11/2021 13:24:54

Title: M87 black hole's image is of 55 million years ago
Post by: Dhruv on 29/11/2021 13:24:54
If the distance between M87's black hole is 55 million light years then it means that the light from the black hole takes 55 million years to reach earth.
So does it mean that the black hole's image we've captured is actually the black hole 55 million years ago. And we don't even know what's happening to the real black hole now
Title: Re: M87 black hole's image is of 55 million years ago
Post by: Halc on 29/11/2021 13:59:16
If the distance between M87's black hole is 55 million light years then it means that the light from the black hole takes 55 million years to reach earth.
Well, it means that light from nearby that black hole takes that long to get here. Black holes don't emit light.

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So does it mean that the black hole's image we've captured is actually the black hole 55 million years ago. And we don't even know what's happening to the real black hole now
Right. That's true of literally anything. We don't know what's happening to the moon right now since the light from it is over one second old, so our latest image of it is from at least one second in the past.
Title: Re: M87 black hole's image is of 55 million years ago
Post by: evan_au on 29/11/2021 21:06:59
Astronomers always look back in time. The bigger the telescope, the farther back in time they can look - which is why astronomers are holding their breath for the launch of the James Webb Space telescope, currently scheduled for end-2021.

We can see that M87 is very active in the light reaching us now. It is possible that the center of M87 had been disrupted by some event (like the merging of two black holes) that sent many stars plunging into the accretion disk. It is possible that it is quieter now, or more active now - we really can't know.

The black hole at the center of the Milky Way is much closer - about 25,000 light years. From the light reaching us now, it looks fairly quiet. But there is evidence that it was much more active in the past, judging by vast clouds of gas above and below the Milky Way galaxy, presumably put there by intense jets of gas from a more active period of the black hole at the center of our galaxy. It is likely that it will activate again, if a large star falls into the accretion disk.
See: https://fermi.gsfc.nasa.gov/science/constellations/pages/bubbles.html