Our own Milky Way has a black hole in its center. The monsters with millions or billions of times the Sun's mass may have grown from smaller black holes called intermediate-mass black holes.
We know that dwarf galaxies have big holes in them. Do all dwarfs have them? It's difficult to say. It's easy to see when a black hole is feeding and goingbbling down material. dwarf galaxies emit a lot of light and can mimic the appearance of a black hole by making stars at high rates.
A new method developed by a team of astronomer does a better job of finding active black holes than the old method. It has shown that there are a lot of black holes in dwarf galaxies.
The methods are not obvious. Astronomers refer to gas clouds in space as lines because they emit light at very specific wavelength. If you want to know more about this process, I wrote about it in an earlier article and covered it in my episode of Crash course Astronomy: Light. Each element in a gas cloud emits light in a set of narrow colors, and this acts like a fingerprint that tells us how hot it is, how dense it is, and more.
The lines are caused by matter swirling around in a black hole and gas clouds forming stars, and it takes a long and complicated chain of measurement to distinguish the two. There is a standard set of line ratios used to look at dwarf galaxies to see if they have active black holes or if they have lots of stars. Either way, or both.
This is the case for a lot of dwarfs. The standard method doesn't work well and could potentially miss a lot of active black holes. They used a different set of line ratios and applied it to a deep survey of the sky that looked at every dwarf galaxy out to a certain distance.
They discovered that a lot of the galaxies they IDed as star-forming are actually making lots of stars and having a black hole. The old method estimated that 1% of all dwarf galaxies were like this, but the new method shows they make up from 3 to 16%. More is more. Almost all the newly found double-duty dwarf galaxies have a low ratio of heavy elements, a sign that the new method has an advantage over the old method.
They were able to make a lot of sub- categories of galaxies, including ones with different types of black hole activity, which can depend on the orientation at which we see the material around it. Calculating the dynamics of what is happening in the hearts of dwarf galaxies is a huge step.
This is important for two things. It is difficult to see dwarf galaxies at great distances because they are so small. Figuring out which ones are harder to study will help the astronomer.
It's believed that big galaxies grow because of eating dwarf galaxies. This happened a lot in the early Universe when the galaxies were closer together, but it still happens today. We need to understand dwarf galaxies if we want to understand how big they are. This is a positive step.
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