Galaxies or Black Holes: A Cosmic Chicken-and-Egg Problem

Author: William Heise

Have you ever wondered whether galaxies form around black holes, or black holes form around galaxies? If yes, read this! In this piece, we will present both sides of the argument. The farthest galaxy we have ever seen is about 14.3 redshift away, which is 13.3 billion light years away! This galaxy shows no sign of a supermassive black hole in its center. This galaxy was discovered by an international team that used the James Webb Space Telescope. The galaxy JADES-GS-z14-0 is really bright for its distance, which is over 1600 light years across (for context, the Milky Way galaxy is 100000 light years across). The question is, why is this galaxy so bright , considering its size?

Credits: Wikipedia/NASA

There has also been no evidence for the existence of a supermassive black hole at the center of the Triangulum galaxy. Although recent evidence suggests that the Large Magellanic Cloud may actually have a central supermassive black hole, so it is not a good example of a galaxy with no black hole in the center. It also has extremely massive stars, including one around 250 times the mass of the Sun, although even if a star like that collapses into a black hole, that would only make a stellar-mass black hole, not a supermassive one. So the galaxy itself did not have to wait for that star to make its central black hole.

This raises the question whether a galaxy really needs a supermassive black hole in its center in order to form, or whether things like gas and dark matter are the more important ingredients at the beginning. The necessary conditions are:

1. enough gas to form stars and build the galaxy

2. dark matter to help gas clouds collapse and stabilize stars in their

   orbits

However, there is also another side to this argument: maybe galaxies need black holes to form. The James Webb Space Telescope has collected data on "little red dots": compact red objects that may be powered by growing black holes, although their exact nature is still being studied. These black holes are about 13 billion light years away, which is the time when the first galaxies formed.

These "little red dots" are extremely compact objects from the early universe, around 1000 - 2000 light years across. Some scientists think they may contain baby supermassive black holes surrounded by dense gas. In that case, the black hole would pull in nearby gas, some of which would orbit around it while some would fall inward and help it grow. Over time, that gas could also cool and collapse into stars. Dark matter would be important, because it helps pull matter together and build the galaxy. And thus, this connects back to the chicken-and-egg question: did galaxies form first and then their black holes, or did black holes help galaxies form around them?

References

1. Galaxy JADES-GS-z14-0 Spectrum (NIRSpec). NASA. https://science.nasa.gov/asset/webb/galaxy-jades-gs-z14-0-spectrum-nirspec/

2. Galaxy JADES-GS-z14-0 Spectrum. ESA. https://www.esa.int/ESA_Multimedia/Images/2024/05/Galaxy_JADES-GS-z14-0_Spectrum

3. Messier 33 (Triangulum). NASA. https://science.nasa.gov/mission/hubble/science/explore-the-night-sky/hubble-messier-catalog/messier-33/

4. Supermassive Black Hole Likely Lurking in Milky Way's Nearest Neighbor. Caltech. https://www.caltech.edu/about/news/supermassive-black-hole-likely-lurking-in-milky-way-galaxys-nearest-neighbor

5. Newfound Galaxy Class May Indicate Early Black Hole Growth, Webb Finds. NASA. https://science.nasa.gov/missions/webb/newfound-galaxy-class-may-indicate-early-black-hole-growth-webb-finds/

6. Massive Black Holes and the Evolution of Galaxies. NASA. https://science.nasa.gov/astrophysics/programs/physics-of-the-cosmos/massive-black-holes-and-the-evolution-of-galaxies/

7. Kormendy and Ho. Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies. Annual Review of Astronomy and Astrophysics, 2013. https://www.annualreviews.org/content/journals/10.1146/annurev-astro-082708-101811