How Big is a Gamma Ray
The estimated size of
a gamma ray burst depends on its distance. Redshift=distance
makes some if not all gamma ray bursts impossibly energetic.
afterglow from a gamma ray burst is centered in this false
color image from the space-based Chandra X-ray Observatory.
While the gamma rays are produced for only a few seconds,
many of these events can be identified by their afterglow in
X-ray, visible light and radio waves. These are often
associated with galaxies at great distances. Astronomers
describe them as the biggest explosions in the universe.
estimated size of a gamma ray burst depends on its distance.
If we think it is far away, the burst will seem much larger
than if we think it is nearby. So when we start seeing "the
biggest explosions in the universe" it behooves us to take
another look at how we determine their distance.
Almost all of
the millions of galaxies are redshifted (there are less than
a dozen known exceptions to this rule.) This means that when
we look at the spectra (rainbows) made of their light, the
lines which identify particular elements are shifted toward
the red (longer wavelengths). In the late 1920's, a few
years after astronomers finally realized that galaxies were
outside of the Milky Way, Edwin Hubble (after whom the
Hubble telescope was named) noticed that there is a
relationship between how big and bright a galaxy is and how
much its light is redshifted. For the hundreds of galaxies
he studied, the big, bright galaxies had low redshifts and
the small faint galaxies had high redshifts. Adding the
assumption that big and bright means closer than small and
faint, astronomers concluded that redshift could be used as
a measure of distance.
Most (but not
all) astronomers also assumed that this galactic redshift is
a measure of velocity (just as a train whistle sounds lower
when it's going away than when it's approaching, light can
become redshifted when the object is going away and
blueshifted when it is approaching.) All of the expanding
universe and big bang theories are based on this assumption,
neatly summed up in the description, "the farther away a
galaxy is, the faster it is moving away."
But does it
work? In the 1960's, Halton Arp began documenting cases
where redshift couldn't possibly mean distance. He was
finding instances where two or more galaxies and/or quasars
were associated, or even physically connected, in
contradiction of the assumption that their different
redshifts meant that one should be millions or even billions
of light-years farther away than the other. He concluded
that using redshift as a measure of distance distorts the
actual distance. The higher the redshift, the greater the
So what does
that mean for the gamma ray bursts? Many of the first gamma
ray bursts identified by their afterglow in the late 1990's
were from galaxies with very high redshift, indicating
distances as far as 12 billion light years. The energy
required to produce the observed flash of gamma-rays from
this distance would be staggering! Nothing observed in our
stellar neighborhood comes close, not even the occasional
supernova. So the question becomes, are the gamma ray bursts
an unknown form of hypernova? Or are the redshift distances
to their host galaxies greatly exaggerated, and the
explosions much smaller?
New light was
shed on this question by a gamma ray burst on December 3rd,
2003 (GRB 031203). This burst was identified with a closer
galaxy, only about 1.3 billion light years away (by the
redshift assumption.) This burst was thoroughly studied for
months by an armada of space and ground-based observatories.
Astronomers concluded that this was the closest cosmic
gamma-ray burst on record, but also the faintest. This led
the researchers to ask whether gamma ray bursts come in a
variety of sizes.
possibility is that the variation of intensity between
distant and nearby gamma ray bursts is one more layer of
evidence that redshift is not an accurate measure of
distance. The high-redshift gamma ray burst and the low-redshift
gamma ray burst may have been of similar intensity, but
astronomer's assumption that one is much farther away has
made it appear much brighter. Since gamma ray bursts are
common events (about one a day is detected, although only a
few are identified with host galaxies), perhaps they will
become the crucial observation that brings the redshift/distance
distortion into better focus.
If that happens,
we will find ourselves living in a completely new universe
that didn't begin in a big bang and isn't expanding. And in
this new universe, galaxies give birth to quasars, which
grow up into new galaxies. The gamma ray bursts may be the
electromagnetic cry of a newborn galaxy.
lecture video, "Intrinsic
Redshift," for more details of this new picture
of the universe.] Available from Mikamar Publishing
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