ERIS MAY AFTER ALL BE SMALLER THAN PLUTO
Space.com
Astronomers are now inclined to believe that the dwarf planet Eris --
once thought to be the largest body in the Solar System beyond
Neptune's orbit -- may actually be smaller than Pluto, which has a
diameter of about 2342 km. A new estimate of the size of Eris could
be made after Eris was observed occulting a star on November 6. It is
still believed that Eris is about 25 per cent more massive than Pluto,
so if Pluto is a bit bigger, or roughly the same size, Eris must be
denser and therefore made of different material, which comes as a
surprise to some astronomers. Eris has a highly elliptical orbit,
reaching nearly 100 AU from the Sun at its farthest point, making it
more than three times as distant as Pluto. It has one known moon.
BARS KILL SPIRAL GALAXIES?
RAS
An international team of scientists has suggested that the bars found
in many spiral galaxies may be helping to kill them off. The
overwhelming majority of stars in the Universe are found in galaxies
like our own Milky Way, each containing the order of 10*12 stars.
Galaxies come in a variety of shapes, from irregular to spirals, where
spiral arms wind out in a disc from a central bulge. About half the
spiral galaxies have a bar -- a linear structure of stars crossing the
centre. Bars are important for the evolution of galaxies, as they
provide a way to move material into and out of the disc and possibly
help to spark star-formation in the central regions. They may even
help to feed the central massive black hole that seems to be present
in many galaxies. But we still do not understand why some galaxies
have bars and others do not.
The team drew on the work of the volunteers taking part in Galaxy 2
(a 'citizen science' project,
www.galaxyzoo.org), a follow-on from the
successful Galaxy Zoo project. The volunteers were asked to make
detailed classifications of the galaxies that they looked at,
including information on the presence of a bar. With those data --
the largest-ever sample of galaxies with visual bar identifications --
they have shown that red spirals are about twice as likely to have
bars as blue spirals. The colours are significant. Blue galaxies get
their hue from the hot young stars they contain, implying that they
are forming stars in large numbers. In red galaxies, star-formation
has slowed or stopped, leaving behind the cooler, long-lived stars
that give them their red colour. For some time data have hinted that
spirals with more old stars are more likely to have bars, but with
such a large number of bar classifications astronomers are much more
confident about that result. The astronomers conclude that bars might
help to kill spiral galaxies, although how they might do that is
unknown.
FERMI TELESCOPE FINDS STRUCTURE IN OUR GALAXY
ScienceDaily
The Fermi gamma-ray space telescope has found a previously unseen
structure in the Milky Way. The feature may be the remnant of an
eruption from a black hole at the centre of our Galaxy. The structure
consists of two gamma-ray-emitting bubbles that extend 25,000
light-years on either of the Galactic Centre and spans more than half
of the visible sky, between the constellations Virgo and Grus. The
team discovered the bubbles by processing publicly available data from
Fermi.
Although hints of them appear in earlier spacecraft data, the bubbles
had not been recognized previously, partly because a fog of gamma rays
appears all over the sky. The fog happens when particles moving near
the speed of light interact with light and interstellar gas in the
Milky Way. The Fermi team constantly refines models to uncover new
gamma-ray sources obscured by that so-called diffuse emission. The
bubble emissions are much more energetic than the gamma-ray fog seen
elsewhere in the Milky Way, and appear to have well-defined edges.
The structure's shape and emissions suggest that it was formed as a
result of a large and relatively rapid energy release -- the source of
which remains unknown. One possibility includes a particle jet from
the super-massive black hole at the Galactic Centre. In some other
galaxies, astronomers see fast-particle jets powered by matter falling
towards a central black hole. While there is no evidence that the
Milky Way's black hole has such a jet today, it may have had one in
the past. The bubbles may instead have formed, again in analogy with
some other galaxies, as a result of gas outflows from a burst of star
formation, perhaps the one that produced many massive star clusters in
the Milky Way's centre several million years ago.
YOUNGEST 'NEARBY' BLACK HOLE OR NEUTRON STAR
NASA
Astronomers using the Chandra X-ray observatory have found evidence of
a black hole only 31 years old in our cosmic neighbourhood. It is a
remnant of SN 1979C, a supernova in the galaxy M100, which is
approximately 50 million light-years away. Chandra, Swift, XMM-Newton
and ROSAT have seen a bright source of X-rays that remained steady
from 1995 to 2007. It is suggested that the object is a black hole
being fed either by material falling into it from the supernova or
from a binary companion. If that interpretation is correct, it is the
nearest place where the birth of a black hole has been observed. The
scientists think that SN 1979C, first discovered by an amateur
astronomer in 1979, formed when a star about 20 times the mass of the
Sun collapsed. Although the evidence seems to point to a newly formed
black hole in SN 1979C, another possibility is that the remnant is a
rapidly spinning neutron star with a powerful wind of high-energy
particles that could be responsible for the X-ray emission. That
would make the object in SN 1979C the youngest and brightest example
of such a 'pulsar wind nebula' and the youngest known neutron star.
The Crab pulsar, the best-known example of a bright pulsar wind
nebula, is about 950 years old.
COSMIC CURIOSITY IS WORKED BY NOW-DEAD QUASAR
Yale University
The once-enigmatic greenish gas cloud called Hanny's Voorwerp (Hanny's
object), discovered in 2007 by the Dutch schoolteacher and 'Galaxy
Zoo' volunteer astronomer Hanny van Arkel, has been discussed in these
Bulletins previously, first in ENB 250 (2008 August) and most recently
in no. 292 (2010 July 18). It is being illuminated by a quasar (active
galactic nucleus) in the adjacent galaxy IC 2497. The quasar appears
to have burnt out, although the light it emitted in the past continues
to illuminate the gas cloud and produce a sort of 'light echo' of the
now-dead quasar. It is estimated that the light from the dead quasar
took up to 70,000 years to reach the Voorwerp, so the quasar must have
shut down within the past 70,000 years -- a surprise, because it has
been assumed that quasars would take millions of years to die down.
Although the galaxy no longer shines brightly in X-ray light as a
quasar, it is still radiating at radio wavelengths. Previous ENBs can
be found at:
LINK DEEP IMPACT LOOKS AT COMET HARTLEY 2
Ball Aerospace, Boulder, Colorado
On November 4 the 'Deep Impact' spacecraft photographed Comet
103P/Hartley 2 as part of the EPOXI mission. The rendezvous with
Hartley 2 is the third mission for the Deep Impact spacecraft. The
first was in 2005 when an impactor launched from the spacecraft
collided with the nucleus of Comet Tempel 1; images of the nucleus and
excavated debris have thrown light on the composition of Tempel 1.
The second was to provide observations of the Earth in both visible
and infrared wavelengths. The main phase of the Comet Hartley 2
mission began on November 3 when the spacecraft was about 18 hours
from the time of closest approach; nearly 5800 images were obtained.
The spacecraft was panned to maintain imaging of the comet nucleus
while at the same time keeping its high-gain antenna pointed towards
the Earth.
HAYABUSA PROBE COLLECTED ASTEROID SAMPLE
BBC News
Japanese scientists have confirmed that particles found inside the
Hayabusa probe after its seven-year space trip are from the asteroid
Itokawa. Japan's space agency JAXA said that microscopic analysis of
1,500 grains retrieved from the craft's sample canister proved that
they were of extra-terrestrial origin. It is the first time that
samples from an asteroid have been returned to Earth. The Hayabusa
mission spent three weeks orbiting asteroid Itokawa in 2005 and
attempted to pluck dust from its surface. No-one was quite sure
whether it had succeeded at the time, because the capture mechanism
appeared to fail just as the craft approached the asteroid's surface.
The Japanese project team were confronted with a number of successive
problems with the spacecraft, but have managed to keep it operational
and bring it back to Earth, albeit three years later than originally
planned.
The sample capsule was delivered safely to Earth over Australia in
June, but the main Hayabusa spacecraft was destroyed on re-entry into
the atmosphere. Scientists at JAXA have subjected minuscule grains
found inside the canister to detailed examination, and say almost all
of them are extra-terrestrial and come from Itokawa. It appears that
Hayabusa must have disturbed the surface of the asteroid sufficiently
in its approach to kick up dust into the probe's capture tool, even
though the mechanism itself did not work as designed. The particles
were found to contain the minerals olivine, pyroxene and plagioclase.
Although those are minerals that are common on Earth, the particles
from Hayabusa are said to be quite different from terrestrial ones,
both in the relative abundances of the minerals and in their atomic
composition. Some also contain the mineral troilite (an iron
sulphide) that has been found in certain meteorites but not on the
surface of the Earth. The Hayabusa particles represent only the
fourth set of extra-terrestrial materials brought to us by spacecraft.
The others include the Moon rocks recovered by US and Soviet missions,
cometary dust captured by the American Stardust probe, and particles
in the solar wind returned by the Genesis spacecraft.
COST OF JAMES WEBB TELESCOPE SOARS
BBC News
The scale of the delay and cost overrun blighting NASA's James Webb
space telescope has been laid bare by a panel called in to review the
project. The group believes that the final budget for Hubble's
successor is likely to climb to at least $6500m, for a launch that may
be possible in 2015. Estimates of the total cost to build, launch and
operate the JWST have increased over the years from $3500m to $5000m
and now to $6500m. Along with the cost growth, the schedule has
slipped, and the most recent projected launch date in 2014 has seemed
unrealistic for some time. The group found the original budget for
the project to be insufficient and poorly phased; it did however
commend the technology of JWST as being "in very good shape".
The telescope is obviously a major undertaking. Its primary mirror is
6.5 metres across -- nearly three times Hubble's aperture. It will
operate behind a large sun-shield, the area of a tennis court, which
will protect it from radiation from the Sun and the Earth. It is to be
launched on a European Ariane-5 rocket and sent to an observing
position 1.5 million km from the Earth, where it cannot be serviced by
astronauts as Hubble has been. Whereas Hubble sees mostly in visible
light, JWST will observe in the infrared. It is expected to have a
10-year lifespan.
Topic: Late November Astronomy Bulletin (Read 750 times)