Information Technology Reference
In-Depth Information
6.4
Supermassive Black Holes
A large number of galaxies have extremely bright galactic centers. These luminous
nuclei of galaxies are known as quasars. Astronomers and cosmologists have long
suspected that black holes are the source of power. The concept of black hole is
derived from Einstein's
General Relativity
. Recent evidence indicated the existence
of
supermassive black holes
at the centers of most galaxies (Richstone et al.
1998
).
In the mass extinction case, searching for conclusive evidence had forged some
of the most significant developments for each competing paradigm. Because those
extinction events happened at least tens of million years ago, it is a real challenge
to establish what had really happened. In our second case study, astronomers faced
a similar challenge. Black holes by definition are invisible. Searching for evidence
that can support theories about the formation of galaxies and the universe has been
a central line of research concerning supermassive black holes. We apply the same
visualization method to the dynamics of citation patterns associated with this topic.
BBC2 broadcasted a 50-min TV program on supermassive black holes in 2000. The
transcripts are available on the Internet.
1
6.4.1
The Active Galactic Nuclei Paradigm
In astronomy, active galactic nuclei (AGN) refers to several extraordinary phe-
nomenon, including quasars, Seyfert galaxies, and radio galaxies. In 1943, Carl
Seyfert published a catalogue of strange galaxies that have bright objects at their
centers and peculiar spectra. Seyfert galaxies have very bright nuclei with strong
emission lines of hydrogen and other common elements, showing velocities of
hundreds or thousands of kilometers per second.
The fundamental question that concerns astronomers is: What is powering these
AGN? A number of theories have been proposed, including starbursts, giant pulsars,
and supermassive black holes. In 1971, Martin Rees and Donlad Lynden-Bell were
among the first to propose that there must be a supermassive black hole hiding in
the galactic center. A supermassive black hole typically weighs between 10
6
and
10
9
times of the sun in our solar system. Now this paradigm for what powers high-
energy active nuclei (AGN) is known as the active galactic nuclei (AGN) paradigm
(Ho and Kormendy
2000
). It is well established through observations and theoretical
arguments.
The AGN paradigm has offered the simplest and consistent explanations so far.
On the other hand, new evidence round the corner may overturn this paradigm
completely, as Kuhn's theory would predict. According to (Kormendy and Rich-
stone
1995
), among others, Terlevich, Filippenko, and Heckman made some of
the strongest arguments against the AGN paradigm. By 2000, as highlighted in
Search WWH ::
Custom Search