SUSPECTED ASTEROID COLLISION
NASA
The Hubble telescope has observed an asteroid associated with an
unusual debris pattern and trailing streamers of dust that suggest a
collision between two asteroids. Astronomers have long thought that
the asteroid belt is being ground down through collisions, but no
evidence has been seen previously of a recent collision. An object
called P/2010 A2 was discovered by the LINEAR sky survey on January 6.
At first, astronomers thought it might be a so-called 'main-belt
comet' -- a rare case of a comet orbiting in the asteroid belt.
Follow-up images taken by Hubble on January 25 and 29, however,
revealed a complex X-pattern of filamentary structures near the
nucleus. Hubble shows the main nucleus of P/2010 A2, estimated to be
140 m across, to lie outside its own halo of dust.
Normal comets are thought to fall into the inner regions of the Solar
System from distant reservoirs and, as they approach the Sun and warm
up, ice near the surface vaporizes and ejects material from the solid
nucleus by jets. But the debris round P/2010 A2 may have a different
origin. The asteroid orbits within the asteroid belt where its
nearest neighbours are dry rocky bodies lacking volatile materials.
It seems possible that the complex debris tail is the result of an
impact between two bodies, rather than ice simply volatilizing from a
parent body. If that interpretation is correct, two small and
previously unknown asteroids recently collided, creating a shower of
debris that is being swept back into a tail from the collision site by
the pressure of sunlight. The main nucleus of P/2010 A2 would be the
surviving remnant of the collision. The asteroid belt contains
abundant evidence of ancient collisions that have shattered precursor
bodies into fragments. The orbit of P/2010 A2 is consistent with
membership in the Flora asteroid family, produced by collisional
shattering more than 100 million years ago.
ASTRONOMERS DISCOVER COOL STARS IN NEARBY SPACE
RAS
Astronomers using the United Kingdom Infrared Telescope (UKIRT) in
Hawaii have discovered what may be the coolest sub-stellar body so far
found outside the Solar System. It has very peculiar colours, which
make it appear either very blue or very red, depending on which part
of the spectrum is considered. The object is known as SDSS1416+13B
and is in a large orbit around a somewhat brighter and warmer brown
dwarf, SDSS1416+13A. The pair is between 15 and 50 light-years away.
The brighter member was detected in visible light by the Sloan Digital
Sky Survey, but SDSS1416+13B is seen only in infrared light.
SDSS1416+13B was first noticed as part of a dedicated search for cool
brown dwarfs by UKIRT. The object appeared far bluer at near-infrared
wavelengths than any brown dwarf seen before. A near-infrared
spectrum taken with the Japanese Subaru telescope in Hawaii showed
that it is a type of brown dwarf called a T dwarf, which has a lot of
methane in its atmosphere, but with peculiar spectral features
including a big gap at a certain wavelength. Astronomers soon noticed
that a previously observed brighter star (SDSS1416+13A) close by is
also a brown dwarf. They then used the orbiting Spitzer telescope to
investigate SDSS1416+13B at mid-infrared wavelengths, which are
thought to be the most reliable indicator of temperature, and found
that it is the reddest known brown dwarf at those wavelengths by some
margin. Comparison with theoretical models of brown-dwarf atmospheres
has provided a temperature estimate of 500 K.
UNUSUAL SUPERNOVA EXPLOSION
Science Daily
For the first time, astronomers have found a supernova explosion with
properties similar to a gamma-ray burst, but without seeing any gamma-
rays from it. Radio observations made with the VLA showed that
material was expelled from the supernova explosion SN2009bb at speeds
approaching that of light. That characterized the supernova, first
seen last March, as the type thought to produce one kind of gamma-ray
burst. When the nuclear-fusion reactions at the cores of very massive
stars can no longer provide the energy needed to hold the core up
against the weight of the rest of the star, the core collapses
catastrophically into a super-dense neutron star or black hole. For
reasons not easy to explain in simple terms, the rest of the star's
material is blasted into space in a supernova explosion. Astronomers
have identified one particular type of such 'core-collapse supernovae'
as the cause of one kind of gamma-ray burst. Only about one out of a
hundred supernovae of that type, however, produces a gamma-ray burst.
In the more-common type of supernova, the explosion blasts the star's
material outward in a roughly spherical pattern at speeds of 'only'
about 3% of that of light, whereas in the supernovae that produce
gamma-ray bursts, some, but not all, of the ejected material is
accelerated to nearly the speed of light. Such extreme speeds are
thought to be caused by an 'engine' in the centre of the supernova
explosion, in which material falling toward the core enters a swirling
'accretion disc' surrounding the new neutron star or black hole. The
disc produces -- still by processes hard to explain -- jets of
material boosted to tremendous speeds from the poles of the disc.
Until now, no such 'engine-driven' supernova had been found by any
other means than by detecting gamma-rays emitted by it. The VLA radio
telescope is soon to be upgraded, and some of the more optimistic
astronomers hope in the future to find more such supernovae through
radio observations than with gamma-ray satellites. One important
question still to be answered is just what causes the difference
between the ordinary supernovae and the 'engine-driven' ones.
BRITAIN WITHDRAWS FROM CASSINI MISSION
BBC News
While the Cassini mission to Saturn is so successful that NASA has
just extended it by seven years, British participation is to end
because a government funding agency has withdrawn support. Scientists
who work on Cassini say that the decision by the Science and
Technology Facilities Council (STFC) will damage British astronomy
severely. They accuse the agency of breaking international
partnerships and jeopardising British involvement in future missions,
just to save about £700,000 a year. The Cassini mission, which
reached Saturn in 2004, is transforming understanding of the planet
and its rings and moons. British scientists are involved in operating
five of its instruments and processing their observations. However,
the STFC, which has a budget shortfall of £115 million, identified
further support as a low priority. The cuts also threaten a
significant British role in future missions. A spokesman for the STFC
said that tight financial budgets had forced unpalatable but necessary
choices to be made to wind down, or to withdraw from, some projects.
Topic: Mid February Astronomy Bulletin (Read 634 times)