What emits light at the centre of galaxies?

176 views

[ad_1]

If I understand correctly, black holes are the centres of galaxies, so what emits light in the centre of galaxies that we see from far away?

In: Physics
[ad_2]

Stars are packed much more densely near the centers of the galaxies, because they are attracted by those black holes. So it’s all those stars all around those black holes that emit the light that we see at the center.

Galaxies don’t have some single hot center light.

They have a cluster of stars near the middle, a few maybe even tightly orbiting the black hole like huge fucky glowing planets. 🙂

But there are only a few right on the black home and thousands/millions more just sorta nearby.

Here is the best real image we have of the dense area kinda near the core of our galaxy.

https://www.nasa.gov/image-feature/goddard/hubble-peers-into-the-most-crowded-place-in-the-milky-way/

I have long wondered what the night sky would look like if our planet were orbiting a star closer to the galaxy center.

As no other answer seems to have covered the actual centre of many galaxies I’ll have a go at it.

The centre of a galaxy is also called a “galactic nucleus” these can have, as you stated, a black hole.

In some instances this very massive black hole, also called a supermassive black hole, turns the “nucleus” into a AGN, an active galactic nucleus.

The most powerful of such AGNs are called “Quasars” and they are literally the most luminous things in the entire observable universe. In fact they can be so luminous that a single quasar is thousands of times brighter than entire galaxies such as our Milky Way.

The black hole in the centre accumulates particles, gas, around it in a so called “accretion disk”. As these particles fall closer to the black hole the temperature of the accretion disk rises due to compression and friction.
As the temperature rises so does the emission of electromagnetic radiation, hence luminosity.

If you think about it, nuclear fusion, the process by which our Sun produces light, converts around 0.67% mass into energy. Now we all agree that the Sun is pretty bright right? The process of accretion however is throught to convert tens of percent up to and even over 40% of mass into energy.

So there you have it, some galaxies have a supermassive black hole in the centre that has a hot glowing accretion disk, which is brighter than the entire galaxy that it is contained in.
Also a small bonus, these AGNs can have “jets” of electromagnetic radiation (like gamma rays) that are directed at us, we call such AGNs “Blazars”. These things, also technically quasars, can be even brighter than a regular quasar.

It’s usually a giant black hole…
Because the star that used to be there has exploded.

But there’s also a chance you can see a giant star in the middle of the galaxy.