Why do pictures of galaxies appear brightest at their center despite the center being a super massive black hole which doesn’t allow light to escape?
Why do pictures of galaxies appear brightest at their center despite the center being a super massive black hole which doesn’t allow light to escape?
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Galaxies have more stars in their central region than on the outskirts. So the center will appear brighter.
The supermassive black hole at the center of a galaxy is, despite its impressive name, not that big in terms of the size of the region where light can’t escape. For example, the distance from which light can’t escape Sagittarius A*, the supermassive black hole at the center of our Milky Way, is far less than the distance between the Earth and the Sun.
So on the scale of an entire galaxy, the Schwarzschild Radius of even a large supermassive black hole is negligible and the brightness profile of the galaxy is determined primarily by the distribution of stars.
If you would take a trillion-pixel image of the Milky Way (1 million squared), our central black hole would be just 0.00002 pixels wide. There are larger black holes, but even the largest one wouldn’t even fill a full pixel.
The center is the brightest region because it has the highest star density.
Bear in mind that a galaxy is a three-dimensional object, thicker in the centre (as well as having higher star density in the centre) which you are viewing from one direction, so the stars in the centre appear near each other to you while in reality they may be on opposite sides (near and far) of the galaxy. This makes the stars look closer together, and the whole galaxy brighter, in the centre, and would happen even if the galaxy was a sphere with uniformly distributed stars (which it is not).
The other answers about brightness of black holes and their size are also correct.