Black hole news

Source: Bad Astronomy | Rogue lone black hole may have been found 5,000 light-years from Earth | SYFY WIRE

Using a combination of huge ground-based telescopic surveys and the keen vision of Hubble Space Telescope, two teams of astronomers have found what may be — may be — a rogue black hole zipping through space about 5,000 light years from Earth.

The science of this is cool, and even more fun is that the two teams disagree with each other over some very fundamental aspects of this. So it’s not clear what’s happening here.

First, a note: I wrote about this in February 2022 when one of the teams put their at the time not yet peer-reviewed paper online. With the publication of the second paper things have changed, though, which is detailed below. [Link to paper 1, link to paper 2]

The discovery relies on what’s called gravitational lensing. I’ve written about this before:

Any object with mass — a galaxy, a star, you, me — bends space, literally warps it. We perceive that bending as gravity. If you shoot a rocket past the Moon, the gravity of the Moon bends the path of that rocket.

This happens with light, too. Like a car following a curve in the road, a photon (a particle of light) traveling through the Universe will have its path slightly bent this way and that as it passes by massive objects. The more massive the object (and the closer the photon flies past it) the more the light gets bent. We call objects like these gravitational lenses, because a lens is an object that bends light.

Galaxies are massive, and can bend light from galaxies even farther away. That’s lensing on a huge scale. But smaller objects like stars and planets can do this too, and we call them microlenses. The stronger the gravity the more intense the event, which means they can be seen even better from things like neutron stars and black holes.

These events are somewhat rare, so the more distant stars you can see at once the better the odds of seeing one. Several surveys over the years have been done looking at places like the center of our Milky Way galaxy, where stars are packed together pretty closely. ​

At one point, I remember reading that black holes may be the source of 'dark matter' that appears to reduce universe expansion. Having a 'speculated' black hole in our neighborhood leads to speculation about risks.

Bob Wilson