Every single massive galaxy has a black hole at its center, and bigger galaxies have bigger black holes. It almost seems like a natural progression, with a bigger galaxy meaning more stars and material to feed a bigger black hole. However, most of that material doesn’t make it to the central black hole. So how does a massive galaxy with hundreds of billions of stars spread out over hundreds of thousands of light years contribute to a black hole that at most is solar system sized?
The answer might lie in another elusive and enigmatic gem of the universe: Dark Matter.
Past research has shown that the mass of a central black hole is correlated to both the total mass of stars in an elliptical galaxy and the mass of the galaxy’s dark matter halo. It has been unclear which one the black hole mass is actually related to.
In a new study of 3,000 Elliptical Galaxies, astronomers used star motions as a tracer to weigh the galaxies’ central black holes. To weigh the dark matter halo, they used X-ray measurements of hot gas, since a larger dark matter halo is correlated with a larger reservoir of hot gas.
It was found that there was a ‘distinct relationship’ between the mass of the black hole and that of the dark matter halo. Why?
We know that giant elliptical galaxies tend to form when smaller galaxies merge. These mergers cause the dark matter haloes of the smaller galaxies to interact. Because the total dark matter outweighs the light matter, it acts as a blue print for the growth of the central black hole.
An interesting thing happened as I was making notes on this story. I found a story that had a contradictory title from four years prior. I gave it a quick read, but if you feel so inclined, its right here. They found that the data had no correlation, and that black holes and dark matter had no causal connection.
This has been on ongoing debate in the astronomical community. I have to do more research on my own to see which paper I agree with. Still, there will likely be a lot of follow up to ensure that we get the data right. It also raises questions about the methods we use to measure the masses of black holes and of dark matter haloes. Are they accurate enough to make these claims?
It’s a good reminder that there are scientists who are doing research to support competing theories, and we have to make sure to scrutinize all evidence, whether we agree with it or not. The most important part is that we are doing sound science, and following what the data actually says. We put aside our ego for the truth, and we change our views to match the best data so that we may find what the universe truly is.