Swift Satellite Setback

September 18, 2003 | The launch of the $160 million Swift
satellite won't come quite as swiftly as might be
desired by aficionados of gamma-ray bursts, or GRBs —
the hyperenergetic explosions the satellite should discover and
document with unprecedented ease. According to principal
investigator Neil Gehrels (NASA/Goddard Space Flight
Center), the two instruments that will study the X-ray and
ultraviolet/visible-light afterglows of GRBs already have
been tested and installed in the spacecraft. However, two
rounds of electronics problems have plagued Swift's Burst
Alert Telescope — the wide-angle camera that will
detect and pinpoint GRBs in the first place, hopefully
several times each week. The workhorse instrument might not
be installed until November.

"At the moment things are going very well," says Gehrels,
who is "pretty confident" that Swift will be ready next
May for launch, riding a Delta rocket from Kennedy
Space Center and assuming a gently inclined, low-Earth
orbit. Swift should be beaming real-time GRB data down to
astronomers worldwide within a month of its launch, which
originally had been scheduled for this October. In the
meantime, some GRB researchers are lobbying NASA to extend
the mission of the $25 million High
Energy Transient Explorer,
or HETE-2, which currently
provides them with fairly rapid coordinates for one or two
GRBs monthly. Currently HETE-2 is funded only through next

Dark Energy Detailed

September 18, 2003 | Another study has just found that "dark energy" is real. The Supernova Cosmology Project, an international consortium of 48 astronomers, has published its newest findings about the changing expansion rate of the universe. Observations of 11 new Type 1a supernovae at large distances (redshifts 0.36 to 0.86) confirm that the expansion of the universe has been speeding up, and at a rate that means dark energy amounts to about 75 percent of all the matter and energy in the cosmos. Also, a lack of interstellar reddening in the supernovae shows, to a new degree of accuracy, that the results are not being thrown off by interstellar absorption within the supernovae's galaxies.

Perhaps most interesting to cosmologists, the team got a rough confirmation of the dark energy's equation of state (the pressure it exerts per unit density), a crucial step toward figuring out what dark energy actually is. The value, "w = –1" to an accuracy of about 25 percent, supports Albert Einstein's decades-old idea of a "cosmological constant" built into space-time itself, and argues against newer ideas of dark energy being some kind of actual substance ("quintessence") that exerts negative gravity.

The group's paper will appear in the Astrophysical Journal. A press release is also available.


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