Astronomers
now have their best-ever view of the most extreme energy in the cosmos with a
new map combining three month's worth of data, a team of scientists said today.
The map is
based on data collected by NASA's Fermi Gamma-ray Space Telescope, which has
scopes and cameras that peer out into the universe — from within our solar
system to galaxies billions
of light-years away — in search of the sources of the highest energy
radiation, called gamma rays.
Gamma rays
sit on the far left of the electromagnetic, or light, spectrum, with shorter
wavelengths and higher energy than ultraviolet light and even X-rays.
The all-sky
image produced by the Fermi team shows us how the cosmos would look if our eyes
could detect radiation 150 million times more energetic than visible light. The
view merges observations from Fermi's Large
Area Telescope (LAT) spanning 87 days, from August 4, 2008, to October 30,
2008.
"Fermi
has given us a deeper and better-resolved view of the gamma-ray sky than any
previous space mission," said Peter Michelson, the lead scientist for the
LAT at Stanford University. "We're watching flares from supermassive black
holes in distant galaxies and seeing pulsars, high-mass binary systems, and
even a globular cluster in our own."
The map
includes one object familiar to everyone: the sun. "Because the sun
appears to move against the background sky, it produces a faint arc across the
upper right of the map," Michelson explained.
During the
next few years, as solar activity increases, scientists expect the sun to
produce growing numbers of high-energy flares. "No other instrument will
be able to observe solar flares in the LAT's energy range," Michelson
said.
From the
map, the Fermi team created a "top 10" list of five sources within
the Milky Way and five beyond our galaxy.
The top
sources within our galaxy include the sun; a star system known as LSI +61 303,
which pairs a massive normal star with a super-dense neutron star; PSR
J1836+5925, which is one of many new pulsars, a type of spinning neutron star
that emits gamma-ray beams; and the globular cluster 47
Tucanae, a sphere of ancient stars 15,000 light-years away.
Top
extragalactic sources include NGC
1275, a galaxy that lies 225 million light years away and is known for
intense radio emissions; the dramatically flaring active galaxies 3C 454.3 and
PKS 1502+106, both more than 6 billion light years away; and PKS 0727-115,
which is thought to be a type of active galaxy called a quasar.
The Fermi
top 10 also includes two sources — one within the Milky Way plane and one
beyond it — that researchers have yet to identify.
A paper
describing the 205 brightest sources the LAT sees has been submitted to The
Astrophysical Journal Supplement.
"This
is the mission's first major science product, and it's a big step toward
producing our first source catalog later this year," said David Thompson,
a Fermi deputy project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md.
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