Andrew Yee
May 17th 06, 11:49 PM
Public Affairs Office
Harvard-Smithsonian Center for Astrophysics
For more information, contact:
David A. Aguilar, Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
Christine Pulliam, Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016
For Release: EMBARGOED until 2:00 p.m. EDT, Wednesday, May 17, 2006
Release No.: 06-15
When Dwarfs Gave Way to Giants
Cambridge, MA -- The first galaxies were small -- about 10,000 times less
massive than the Milky Way. Billions of years ago, those mini-furnaces
forged a multitude of hot, massive stars. In the process, they sowed the
seeds for their own destruction by bathing the universe in ultraviolet
radiation. According to theory, that radiation shut off further dwarf galaxy
formation by both ionizing and heating surrounding hydrogen gas. Now,
astronomers Stuart Wyithe (University of Melbourne) and Avi Loeb
(Harvard-Smithsonian Center for Astrophysics) are presenting direct evidence
in support of this theory.
Wyithe and Loeb showed that fewer, larger galaxies, rather than more
numerous, smaller galaxies, dominated the billion-year-old universe. Dwarf
galaxy formation essentially shut off only a few hundred million years after
the Big Bang.
"The first dwarf galaxies sabotaged their own growth and that of their
siblings," says Loeb. "This was theoretically expected, but we identified
the first observational evidence for the self-destructive behavior of early
galaxies."
Their research is being reported in the May 18, 2006 issue of Nature.
Nearly 14 billion years ago, the Big Bang filled the universe with hot
matter in the form of electrons and hydrogen and helium ions. As space
expanded and cooled, electrons and ions combined to form neutral atoms.
Those atoms efficiently absorbed light, yielding a pervasive dark fog
throughout space. Astronomers have dubbed this era the "Dark Ages."
The first generation of stars began clearing that fog by bathing the
universe in ultraviolet radiation. UV radiation splits atoms into negatively
charged electrons and positively charged ions in a process called
ionization. Since the Big Bang created an ionized universe that later became
neutral, this second phase of ionization by stars is known as the "epoch of
reionization." It took place in the first few hundred million years of
existence.
"We want to study this time period because that's when the primordial soup
evolved into the rich zoo of objects we now see," said Loeb.
During this key epoch in the history of the universe, gas was not only
ionized, but also heated. While cool gas easily clumps together to form
stars and galaxies, hot gas refuses to be constrained. The hotter the gas,
the more massive a galactic "seed" must be to attract enough matter to
become a galaxy.
Before the epoch of reionization, galaxies containing only 100 million solar
masses of material could form easily. After the epoch of reionization,
galaxies required more than 10 billion solar masses of material to be
assembled.
To determine typical galaxy masses, Wyithe and Loeb looked at light from
quasars -- powerful light sources visible across vast distances. The light
from the farthest known quasars left them nearly 13 billion years ago, when
the universe was a fraction of its present age. Quasar light is absorbed by
intervening clouds of hydrogen associated with early galaxies, leaving
telltale bumps and wiggles in the quasar's spectrum.
By comparing the spectra of different quasars along different lines of
sight, Wyithe and Loeb determined typical galaxy sizes in the infant
universe. The presence of fewer, larger galaxies leads to more variation in
the absorption seen along various lines of sight. Statistically, large
variation is exactly what Wyithe and Loeb found.
"As an analogy, suppose you are in a room where everybody is talking,"
explains Wyithe. "If this room is sparsely populated, then the background
noise is louder in some parts of the room than others. However if the room
is crowded, then the background noise is the same everywhere. The fact that
we see fluctuations in the light from quasars implies that the early
universe was more like the sparse room than the crowded room."
Astronomers hope to confirm the suppression of dwarf galaxy formation using
the next generation of telescopes -- both radio telescopes that can detect
distant hydrogen and infrared telescopes that can directly image young
galaxies. Within the next decade, researchers using these new instruments
will illuminate the "Dark Ages" of the universe.
Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists, organized into six research divisions, study the origin,
evolution and ultimate fate of the universe.
Note to editors:
High-resolution artwork to accompany this release is available online at
http://www.cfa.harvard.edu/press/pr0615image.html
Harvard-Smithsonian Center for Astrophysics
For more information, contact:
David A. Aguilar, Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
Christine Pulliam, Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016
For Release: EMBARGOED until 2:00 p.m. EDT, Wednesday, May 17, 2006
Release No.: 06-15
When Dwarfs Gave Way to Giants
Cambridge, MA -- The first galaxies were small -- about 10,000 times less
massive than the Milky Way. Billions of years ago, those mini-furnaces
forged a multitude of hot, massive stars. In the process, they sowed the
seeds for their own destruction by bathing the universe in ultraviolet
radiation. According to theory, that radiation shut off further dwarf galaxy
formation by both ionizing and heating surrounding hydrogen gas. Now,
astronomers Stuart Wyithe (University of Melbourne) and Avi Loeb
(Harvard-Smithsonian Center for Astrophysics) are presenting direct evidence
in support of this theory.
Wyithe and Loeb showed that fewer, larger galaxies, rather than more
numerous, smaller galaxies, dominated the billion-year-old universe. Dwarf
galaxy formation essentially shut off only a few hundred million years after
the Big Bang.
"The first dwarf galaxies sabotaged their own growth and that of their
siblings," says Loeb. "This was theoretically expected, but we identified
the first observational evidence for the self-destructive behavior of early
galaxies."
Their research is being reported in the May 18, 2006 issue of Nature.
Nearly 14 billion years ago, the Big Bang filled the universe with hot
matter in the form of electrons and hydrogen and helium ions. As space
expanded and cooled, electrons and ions combined to form neutral atoms.
Those atoms efficiently absorbed light, yielding a pervasive dark fog
throughout space. Astronomers have dubbed this era the "Dark Ages."
The first generation of stars began clearing that fog by bathing the
universe in ultraviolet radiation. UV radiation splits atoms into negatively
charged electrons and positively charged ions in a process called
ionization. Since the Big Bang created an ionized universe that later became
neutral, this second phase of ionization by stars is known as the "epoch of
reionization." It took place in the first few hundred million years of
existence.
"We want to study this time period because that's when the primordial soup
evolved into the rich zoo of objects we now see," said Loeb.
During this key epoch in the history of the universe, gas was not only
ionized, but also heated. While cool gas easily clumps together to form
stars and galaxies, hot gas refuses to be constrained. The hotter the gas,
the more massive a galactic "seed" must be to attract enough matter to
become a galaxy.
Before the epoch of reionization, galaxies containing only 100 million solar
masses of material could form easily. After the epoch of reionization,
galaxies required more than 10 billion solar masses of material to be
assembled.
To determine typical galaxy masses, Wyithe and Loeb looked at light from
quasars -- powerful light sources visible across vast distances. The light
from the farthest known quasars left them nearly 13 billion years ago, when
the universe was a fraction of its present age. Quasar light is absorbed by
intervening clouds of hydrogen associated with early galaxies, leaving
telltale bumps and wiggles in the quasar's spectrum.
By comparing the spectra of different quasars along different lines of
sight, Wyithe and Loeb determined typical galaxy sizes in the infant
universe. The presence of fewer, larger galaxies leads to more variation in
the absorption seen along various lines of sight. Statistically, large
variation is exactly what Wyithe and Loeb found.
"As an analogy, suppose you are in a room where everybody is talking,"
explains Wyithe. "If this room is sparsely populated, then the background
noise is louder in some parts of the room than others. However if the room
is crowded, then the background noise is the same everywhere. The fact that
we see fluctuations in the light from quasars implies that the early
universe was more like the sparse room than the crowded room."
Astronomers hope to confirm the suppression of dwarf galaxy formation using
the next generation of telescopes -- both radio telescopes that can detect
distant hydrogen and infrared telescopes that can directly image young
galaxies. Within the next decade, researchers using these new instruments
will illuminate the "Dark Ages" of the universe.
Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists, organized into six research divisions, study the origin,
evolution and ultimate fate of the universe.
Note to editors:
High-resolution artwork to accompany this release is available online at
http://www.cfa.harvard.edu/press/pr0615image.html