Scientists reach a surprising conclusion about black holes
Which came first: black holes or galaxies? Researchers have wondered for years, and now they think they have an answer.
Astronomers think they have finally solved the cosmic chicken-and-egg problem of what came first -- the giant black holes lying at the center of many big galaxies or the galaxies that feed them?
The answer: the black holes.
The finding, which surprised even the scientists involved, implies that black holes grow the galaxies around them, like a garden springing from a single seed or a man growing his suit of clothes.
The problem with that idea, according to the scientific team who presented the findings at the American Astronomical Society meeting in Long Beach today, is that nobody has yet come up with an explanation for how a black hole could grow a galaxy.
"That is hard to imagine," said Chris Carilli, of the National Radio Astronomy Observatory.
A black hole is the remains of a giant star that has exploded in a supernova and then collapsed to what is known as a singularity, in which the gravity is so extreme that nothing, not even light, can escape. The researchers based their work on past studies showing that for any given galaxy there is a constant ratio between the masses of a central black hole and the so-called "bulge" of stars and gas located relatively close to the center of a galaxy.
In the nearby universe, that ratio is the same for black holes ranging from a few million times the mass of the sun to behemoths billions of times its mass, as is the case with the gigantic black hole in our own Milky Way galaxy.
"The big question," according to Caltech astronomer Dominik Riechers, "has been whether one grows before the other or if they grow together."
To find out, Carilli, Riechers and others on their team used telescopes that capture radio waves instead of visible light to study the first galaxies in the universe, those dating to the time when the universe, which is now 13.7 billion years old, was less than 1 billion years old.
They found these ancient galaxies by studying the degree to which their light was shifted toward the red end of the spectrum. The greater the redshift, which is a measure of how fast the galaxy is speeding away from us, the older the galaxy.
Next, they weighed the black hole and the galaxy's bulge, a challenging calculation that is done by observing the movements of the galaxy's clouds of gas, which are influenced by gravity. In four different young galaxies, the ratio between the black hole and the galaxy bulge was different from what was expected, the scientists said.
