Two teams of astronomer used a combination of ground-based surveys and Hubble Space Telescope to find a black hole that may be 5,000 light years away.
The science of this is cool, and even more fun is that the two teams disagree on some aspects of this. It's not clear what's going on here.
I wrote about this in February of 2020 when one of the teams put their paper online. Things have changed since the second paper was published. There are two links to paper 1 and paper 2.
The discovery is based on a type of lensing. I wrote about this in the past.
Anything with mass warps space. The bending is seen as gravity by us. The moon's gravity bends the path of a rocket if it is shot past it.
This can happen with light as well. Like a car following a curve in the road, a photon will have its path slightly bent as it travels through the Universe. The more massive the object, the closer the photon flies past it. The object that bends light is called a lens.
Light can be bent from far away by Galaxies. That is on a large scale. Microlenses are smaller objects that can do this. They can be seen better from things like black holes and neutron stars if the gravity is strong.
The more distant the stars, the better the chance of seeing one. A lot of surveys have been done looking at the center of the Milky Way.
The OGLE was one of the two surveys that spotted a lensing event. I will call it the event because it was given different names.
A faint, reddish star is between us and the center of the universe, between 20,000 and 26,000 light years away. It was seen to be brighter by a factor of 15 to 100 depending on the observatory used and then fade. It took about 300 days, which is a lot longer than a normal lens. This means it was a very small source with strong gravity. I'm pretty sure.
The star didn't change his color. If the object was a star, its own color would have changed the background star's color. The object was not emitting light since there was no color change.
Critically, the mass, distance, andvelocity of the foreground lensing object can be found by looking at how the star's brightness changes over time as well as how much of its light was diverted by the lens. The surveys give the former characteristics, but Hubble had to use it to measure it. There are problems even then.
One of the teams used Hubble to look at the data, but the other didn't. How long it took, how far away the object is, and the fact that it is a compact stellar-mass object are some of the things they agree on.
They differ.
The object has a mass of 7.1 1.3 times the Sun's. It isunambiguous that a black hole could have that much mass.
The other team has a lower mass range than the Suns. Yes, at the high end. The object could be a neutron star. They can't say what they want to say.
Which one is it. We don't have a clue. It is difficult to say firmly at this time.
It doesn't get better. They see the star moving in different directions when they use Hubble to look at it. The star's position moved slightly east and west. It is troubling. Even with Hubble, it is very difficult to measure the small motion.
One team has a speed of 45 kilometers per second while the other has a speed of 30.
These numbers are so reprehensible that I can't help but feel uneasy. The event is definitely real. We need to be a bit more circumspect about the exact characteristics of what happened. There is a chance it is a black hole or a star.
One team wants to use an additional set of Hubble observations to make sure they can tighten things up. You can't repeat an event like this so more observations won't help It is1-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-6556
If an exciting one, this is a mystery for now. It shows that multiple observations with multiple observatories can be used to find out what is causing these events. It shows that it is very difficult. Future events will hopefully make stronger statements.
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