| |
EI2GYB > ASTRO 09.09.21 20:20l 78 Lines 3633 Bytes #999 (0) @ WW
BID : 14285_EI2GYB
Read: GUEST
Subj: White Dwarfs Still Burn
Path: IW8PGT<IZ3LSV<IR1UAW<IW2OHX<UA6ADV<I0OJJ<EA2RCF<LU9DCE<LU1HVK<W0ARP<
AL0Y<KD8FMR<PY2BIL<EI2GYB
Sent: 210909/1817Z @:EI2GYB.DGL.IRL.EURO #:14285 BPQ6.0.22
_ _ _ _
/ \ ___| |_ _ __ ___ | \ | | _____ _____
/ _ \ / __| __| '__/ _ \ | \| |/ _ \ \ /\ / / __|
/ ___ \\__ \ |_| | | (_) | | |\ | __/\ V V /\__ \
/_/ \_\___/\__|_| \___/ |_| \_|\___| \_/\_/ |___/
White Dwarfs Still Burn
When stars near the end of their lives, they stop burning. Without nuclear
fusion to fend off the press of gravity, most stars will shed their outer
layers before collapsing into white dwarfs.
These crushed remnants, no larger than Earth, support themselves against
further collapse via the exotic physics of electron degeneracy. But they have
no source of energy - or light. They should slowly cool and dim, or so the
theory goes.
Now, ultraviolet Hubble Space Telescope observations of two ancient clusters
show that the steady cooling of white dwarfs isn't so steady after all. And
that's because some of them do, in fact, still burn.
The globular clusters M3 and M13 are both about 13 billion years old. But
despite the clusters' similar age and appearance, Jianxing Chen (University of
Bologna, Italy) and colleagues find that M13 has extra white dwarfs. That
abundance, they show, originates in the cluster's relatively larger number of
weensy stars, those with less than about half the Sun's mass. Even after they
collapse, these stars will retain an envelope of hydrogen for later burning -
in effect, a security blanket of thermonuclear fusion that keeps them warm over
the ages.
About 70% of the white dwarfs in M13 are of the slow-burn variety, still fusing
hydrogen on their surfaces. The finding upsets the notion of white dwarfs as
inert, forever-cooling embers. Read more in the Hubble Space Telescope press
release and in Nature Astronomy.
X-ray Magnifying Glass
The Chandra X-ray Observatory has detected 24 X-ray photons that have traveled
12 billion years from a supermassive black hole . In fact, we'd see even less
than that if not for an intervening galaxy, which acted as a cosmic magnifying
glass and redirected some photons toward Earth.
Yet with just two-dozen photons, Daniel Schwartz (Center for Astrophysics,
Harvard & Smithsonian) and colleagues have sussed out the nature of the
X-ray-emitting system, known as MGB 2016+112. The most likely scenario is that
two galaxies have come together some 2 billion years after the Big Bang, and
their respective supermassive black holes are in the process of merging. They
emit copious amounts of X-rays, many of which are absorbed in swirling gas
surrounding the pair. The black holes currently orbit each other 650
light-years apart. Eventually, this hefty duo will unite, radiating
gravitational waves in the process.
It's possible that what the astronomers are seeing is actually a single black
hole and the very beginning of its thousand-light-year-long jet, rather than a
second black hole. Follow-up spectroscopy will help distinguish between these
two scenarios.
More information on this system is available in the Chandra press release and
the study preprint.
____ __ ____ ___ _ _ ____ ____ ____ ____
( __)( )(___ \ / __)( \/ )( _ \ ( _ \( _ \/ ___)
) _) )( / __/( (_ \ ) / ) _ ( ) _ ( ) _ (\___ \
(____)(__)(____) \___/(__/ (____/ (____/(____/(____/
PART OF THE DONEGAL PACKET RADIO NETWORK
Packet: EI2GYB@EI2GYB.DGL.IRL.EURO
Email: EI2GYB@GMAIL.COM
+------------------------------------------------------------------------------+
Read previous mail | Read next mail
| |
