How can we see a black hole in the middle of the Milky Way?

> How can we see a black hole in the middle of the Milky Way?

Hello,

You ask a very good question. The presence of a black hole in the center
of our galaxy is very controversial, but most astronomers think there is
one there.

With a "normal" (optical light) telescope, we cannot see the center of
the galaxy. The problem is not just a lot of stars, but also the
presence of dust. Dust absords light very well, and so no optical light
from the center of our galaxy can get through. However, infrared light,
radio waves, and x-rays can all pass through dust fairly easily. So, by
looking in these wavelengths of light, astronomers can see the center of
the galaxy.

At the center of the galaxy, astronomers see a couple of things. First,
we can see stars orbitting the center of the galaxy. Using Newton's laws
of physics, we know that the stars are orbitting something that weighs
more than one million times the mass of the sun. In the center of these
star's orbits, we see a bright radio and x-ray source. The size and
brightness of this source agrees well with what astronomers would expect
for a giant disk of gas swirling around a black hole of one million solar
masses.

There are other possibilities for what this mass could be. It could be a
large clump of stars. However, we do not see any infrared light from
such a cluster. In addition, the stars would be so close together that
they would quickly merge to form a black hole.

The second theory is that there is a giant clump of dark matter. This
theory is hard to test, since we cannot see dark matter, but current
theories of dark matter find it hard to explain how a large clump could
form and not form a black hole.

You mentioned the possibility of a "white hole" A white hole is a
theoretical object which is the opposite of a black hole, and would spew
forth large amounts of matter and light. Unfortunately, there is little
evidence for lots of matter and light to be coming out of the galactic
center. There are two jets of gas coming out of the area, but jets are
often formed when gas falls into a black hole. Some gas gets swallowed
up, and some gets flung away in a giant jet.

The available evidence seems to indicate that there is actually a black
hole in the center of our galaxy, and in most other galaxies. But,
because of the difficulty in seeing the galactic center, we can never be
fully certain!

Thanks for writing!

Sincerely,

Kurtis Williams

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