Taking a CAT Scan of the Early Universe (Forwarded)

From: Andrew Yee (ayee_at_nova.astro.utoronto.ca)
Date: 11/17/04 

Date: Wed, 17 Nov 2004 14:58:59 -0500

Harvard-Smithsonian Center for Astrophysics

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Harvard-Smithsonian Center for Astrophysics
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Christine Pulliam, Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
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For Release: Embargoed until 1:00 p.m. EST, November 10, 2004

Release No.: 04-33

Taking a CAT Scan of the Early Universe

Cambridge, MA -- The invention of the CAT scan led to a revolution in medical
diagnosis. Where X-rays give only a flat two-dimensional view of the human body,
a CAT scan provides a more revealing three-dimensional view. To do this, CAT
scans take many virtual "slices" electronically and assemble them into a 3D picture.

Now a new technique that resembles CAT scans, known as tomography, is poised to
revolutionize the study of the young universe and the end of the cosmic "dark
ages." Reporting in the Nov. 11, 2004, issue of Nature, astrophysicists J.
Stuart B. Wyithe (University of Melbourne) and Abraham Loeb (Harvard-Smithsonian
Center for Astrophysics) have calculated the size of cosmic structures that will
be measured when astronomers effectively take CAT scan-like images of the early
universe. Those measurements will show how the universe evolved over its first
billion years of existence.

"Until now, we've been limited to a single snapshot of the universe's childhood
-- the cosmic microwave background," says Loeb. "This new technique will let us
view an entire album full of the universe's baby photos. We can watch the
universe grow up and mature."

Slicing Space

The heart of the tomography technique described by Wyithe and Loeb is the study
of 21-centimeter-wavelength radiation from neutral hydrogen atoms. In our own
galaxy, this radiation has helped astronomers to map the Milky Way's spherical
halo. To map the distant young universe, astronomers must detect 21-cm radiation
that has been redshifted: stretched to longer wavelengths (and lower
frequencies) by the expansion of space itself.

Redshift is directly correlated to distance. The farther a cloud of hydrogen is
from the Earth, the more its radiation is redshifted. Therefore, by looking at a
specific frequency, astronomers can photograph a "slice" of the universe at a
specific distance. By stepping through many frequencies, they can photograph
many slices and build up a three-dimensional picture of the universe.

"Tomography is a complicated process, which is one reason why it hasn't been
done before at very high redshifts," says Wyithe. "But it's also very promising
because it's one of the few techniques that will let us study the first billion
years of the universe's history."

A Soap Bubble Universe

The first billion years are critical because that is when the first stars began
to shine and the first galaxies began to form in compact clusters. Those stars
burned hotly, emitting huge amounts of ultraviolet light that ionized nearby
hydrogen atoms, splitting electrons from protons and clearing away the fog of
neutral gas that filled the early universe.

Young galaxy clusters soon were surrounded by bubbles of ionized gas much like
soap bubbles floating in a tub of water. As more ultraviolet light flooded
space, the bubbles grew larger and gradually merged together. Eventually, about
a billion years after the Big Bang, the entire visible universe was ionized.

To study the early universe when the bubbles were small and the gas mostly
neutral, astronomers must take slices through space as if slicing a block of
swiss cheese. Loeb says that just as with cheese, "if our slices of the universe
are too narrow, we'll keep hitting the same bubbles. The view will never change."

To get truly useful measurements, astronomers must take larger slices that hit
different bubbles. Each slice must be wider than the width of a typical bubble.
Wyithe and Loeb calculate that the largest individual bubbles reached sizes of
about 30 million light-years across in the early universe (equivalent to more
than 200 million light-years in the expanded universe of today). Those crucial
predictions will guide the design of radio instruments to conduct tomographical
studies.

Astronomers soon will test Wyithe and Loeb's predictions using an array of
antennas tuned to operate at the 100-200 megahertz frequencies of redshifted
21-cm hydrogen. Mapping the sky at these frequencies is extremely difficult
because of manmade interference (TV and FM radio) and the effects of the earth's
ionosphere on low-frequency radio waves. However, new low-cost electronics and
computer technologies will make extensive mapping possible before the end of the
decade.

"Stuart and Avi's calculations are beautiful because once we have built our
arrays, the predictions will be straightforward to test as we take our first
glimpses of the early universe," says Smithsonian radio astronomer Lincoln
Greenhill (CfA).

Greenhill is working to create those first glimpses through a proposal to equip
the National Science Foundation's Very Large Array with the necessary receivers
and electronics, funded by the Smithsonian. "With luck, we will create the first
images of the shells of hot material around several of the youngest quasars in
the universe," says Greenhill.

Wyithe and Loeb's results also will help guide the design and development of
next-generation radio observatories being built from the ground up, such as the
European LOFAR project and an array proposed by a US-Australian collaboration
for construction in the radio-quiet outback of Western Australia.

Images to accompany this release are available online at
      http://www.cfa.harvard.edu/press/pr0433image.html

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.

Relevant Pages

  • When Dwarfs Gave Way to Giants (Forwarded)
    ... Harvard-Smithsonian Center for Astrophysics ... Wyithe and Loeb showed that fewer, larger galaxies, rather than more numerous, smaller galaxies, dominated the billion-year-old universe. ...
    (sci.astro)
  • When Dwarfs Gave Way to Giants (Forwarded)
    ... Harvard-Smithsonian Center for Astrophysics ... Wyithe and Loeb showed that fewer, larger galaxies, rather than more ... numerous, smaller galaxies, dominated the billion-year-old universe. ...
    (sci.space.news)
  • The First Stars (Forwarded)
    ... Harvard-Smithsonian Center for Astrophysics ... MA -- The universe began with the Big Bang about 13.7 billion ... the first stars formed. ...
    (sci.space.news)
  • Growing Supermassive Black Holes from Seeds (Forwarded)
    ... Harvard-Smithsonian Center for Astrophysics ... Growing Supermassive Black Holes from Seeds ... discovery that will help in understanding the early universe. ...
    (sci.space.news)
  • Re: All answers to C S Lewis
    ... astrophysics: ... galaxies-very massive and very old-in the universe when it was only ... interstellar space has astronomers running hot and cold. ... - Moons circle planets, ...
    (talk.origins)