STAR MAY HAVE ENGULFED PLANET
BBC News
A US-Polish-Spanish consortium has been using the Hobby-Eberly
telescope in Texas to observe the red-giant star BD +48° 740. Rising
temperatures near the cores of red giants cause them to expand; any
nearby planets will be engulfed. The consortium suggests that that
has happened in the case of their star, merely because of that star's
chemical composition. It contains an abnormally high amount of
lithium, an element created primarily during the Big Bang 14 billion
years ago. Lithium is easily destroyed in stars, so its high
abundance in an old star is unusual. Theoreticians have identified
only a few circumstances, other than the Big Bang, under which lithium
can be created in stars. In the case of BD +48° 740, they suggest
that lithium production might have been triggered by a mass of the
order of a planet that was engulfed by the star and heated it up while
the star was digesting it. Another piece of 'evidence', which is if
anything even more circumstantial than the first, is the highly
elliptical orbit of a newly discovered planet, at least 1.6 times the
mass of Jupiter, around the red giant. Orbits so eccentric are
uncommon in planetary systems around evolved stars, and the
BD +48° 740 planet's orbit is the most elliptical determined so far.
The consortium notes that gravitational interactions between planets
may be responsible for peculiar orbits.
SUGAR MOLECULES FOUND AROUND YOUNG STAR
ESO
Astronomers using the Atacama Large Millimetre Array (ALMA, a radio
telescope still in course of construction in the Chilean Andes)
have observed a young binary star, with a mass similar to the
Sun's, called IRAS 16293-2422. They have identified molecules of
glycolaldehyde -- a simple form of sugar -- in the surrounding gas.
Glycolaldehyde has been seen in interstellar space before, but this is
the first time it has been found so near to a Sun-like star, at
distances comparable to the distance of Uranus from the Sun. The gas
and dust clouds that collapse to form new stars are extremely cold,
and many gases solidify as ice on the particles of dust, where they
then bond together and form more-complex molecules. But once a star
has been formed in the middle of a cloud of gas and dust, it heats the
inner parts of the cloud to around room temperature, evaporating the
chemically complex molecules, and forming gases that emit their
characteristic radiation as radio waves that can be mapped with radio
telescopes such as ALMA. IRAS 16293-2422 got onto the astronomers'
programme of studying the molecules and chemistry around young stars
through its location around 400 light-years away, comparatively
'close' to the Earth.
DOUBLE-STAR SYSTEMS CAN HOST PLANETS
Science
Astronomers using the Kepler telescope have for the first time
discovered two planets orbiting a binary-star system. Kepler had to
date detected four systems each with one circum-binary planet, but now
Kepler 47 has been found as the first system with more than one.
Kepler 47 and its planets, called Kepler 47b and Kepler 47c, are about
5,000 light-years away, in the constellation Cygnus. Many of the
stars in the Galaxy are in binary or higher-order multiple systems,
so the fact that planetary systems can exist in such systems is of
interest. The planets were discovered by the drop in brightness
caused when they transited in front of their star. The dimming is
tiny, only 0.08% for planet b and 0.2% for planet c. For comparison,
Venus blocked about 0.1% of the Sun's surface during its recent
transit.
One of the stars in the binary system is much like our Sun, and the
other is about a third its size and 175 times fainter. The inner and
outer planets are respectively 3 and 4.6 times Earth's diameter. The
smaller one is the smallest circumbinary planet seen yet; it completes
an orbit every 49.5 days, while the outer one takes 303.2 days. The
stars themselves circulate around each other every 7.5 days. It was
already known mathematically that planetary systems can exist round
binary stars, but finding an actual example shows that they can form
there too. Planets are thought mostly to form from a residual disc of
debris left over from the star-formation process, and it is not
obvious that the disc could survive near a newly formed binary star,
owing to the orbital motions of the stars. However, it now appears
that, apart from minor differences in the orbital spacings, planetary
systems around binary stars can be similar to those around single
stars.
41 MORE EXOPLANETS DISCOVERED BY KEPLER
Science Daily
Two newly submitted studies from Kepler verify 41 new transiting
planets in 20 star systems. The results add more than 50% to the
number of Kepler's confirmed planets, to 116 planets in a total of 67
systems, over half of which contain more than one planet. Nineteen of
the newly validated planetary systems have two closely spaced
transiting planets and one system has three. Five of the systems are
common to both of the independent studies. The planets range from
Earth-size to more than seven times the radius of the Earth, but
generally orbit so close to their parent stars that they would be
too hot to live on. The planets were confirmed by analyzing Transit
Timing Variations (TTVs). In closely packed systems, the
gravitational pull of the planets causes the acceleration and
deceleration of a planet along its orbit, making the orbital period of
each planet to change from one orbit to the next. TTVs demonstrate
that two transiting planet candidates are in the same system and that
their masses are planetary in nature. The two research teams used
data from the Kepler space telescope, which constantly measures the
brightness of more than 150,000 stars, to search for transiting
planets. The sheer volume of planet candidates being identified by
Kepler is inspiring teams to look at the planet confirmation and
characterization process differently. The TTV confirmation technique
can be applied to large numbers of systems relatively quickly and
needs little or no follow-up observations from the ground.
GRAVITY WAVES FROM WHITE-DWARF PAIR
BBC News
Researchers have found visible-light evidence for one of astronomy's
most esoteric concepts -- gravity waves. A change in the orbits of
two white dwarf stars orbiting one another 3,000 light-years away is
evidence that such waves occur. Gravitational waves were a
significant part of Albert Einstein's general theory of relativity,
which viewed space itself as a malleable construct, and the gravity of
massive objects as a force that could effectively warp it. The effect
is far too small to be measurable in Earth-bound experiments, but the
wider Universe provides a laboratory in which indirect effects of
gravity waves might be measured. In principle, any two massive
objects orbiting one another can emit gravitational waves, slowly
losing their orbital energy into the waves. The effect is to change
the size and period of the orbit slightly. A measurement of a
minuscule change in the orbits of rapidly rotating neutron stars
garnered the 1993 Nobel Prize in physics.
It is the extreme nature of the pair of white-dwarf stars known as
J0651 -- each a substantial fraction of the Sun's mass orbiting each
other at a distance just a third of that between the Earth and Moon --
that produces observable effects of gravity waves. In 2011, it was
reported that the orbital period of the pair was less than 13 minutes.
Since that discovery, the team has been keenly watching the pair
eclipse one another, with each briefly blocking out the other's light
as seen from here. Over a period of 13 months, the team saw the
orbital period decline by some six seconds -- a tremendous rate of
change, and one that was easily measured. The result was established
in part by a telescope nearly as old as Einstein's theory -- the Otto
Struve 2.1-m telescope at the McDonald Observatory in Texas. The team
will continue to monitor the pair's orbital period.
OBSERVATIONS OF TYPE 1a SUPERNOVA PROGENITOR SYSTEM
Science Daily
Exploding stars called Type 1a supernovae are used for measuring
cosmic distances because they are bright enough to observe across the
Universe and are supposed to have the same luminosity everywhere.
Although astronomers have various theories about the kinds of stars
that give rise to such explosions (the progenitor systems), no one has
ever directly observed one -- until now. The multi-institutional
'Palomar Transient Factory' (PTF) team has collected evidence
indicating that the progenitor system of a Type 1a supernova, called
PTF 11kx, contains a red-giant star. It also shows that the system
previously underwent at least one much smaller nova eruption before it
blew up as a supernova. The system is located 600 million light-years
away in the constellation Lynx. By comparison, indirect observations
of another Type 1a supernova progenitor system (called SN 2011fe,
conducted by the PTF team last year) showed no evidence of a red-giant
star. Taken together, the observations suggest that, just because
Type 1a supernovae look the same, they don't all necessarily arise in
the same way. We know that they do vary slightly from galaxy to
galaxy, and astronomers have been trying to calibrate that, but the
new PTF observation may be providing the first suggestion of why that
happens. It is a surprise to find that thermonuclear supernovae,
which all seem so similar, may seem to come from different kinds of
stars. Although Type 1a supernovae are rare, occurring maybe once or
twice a century in a typical galaxy, finding a Type 1a progenitor
system like PTF 11kx is even rarer.
The PTF survey uses a CCD mosaic in place of a photographic plate on
the 48-inch Schmidt telescope at Palomar to scan the sky repeatedly
and look for changes. The data go to a computer in Berkeley which
identifies events for scientists to follow up. The computer detected
the supernova on 2011 January 16, and astronomers at the Lick
Observatory promptly obtained spectra, which showed strong calcium
absorption lines in the gas and dust surrounding the supernova. Later
observations made with the Keck Telescope in Hawaii indicated that the
clouds of gas and dust surrounding PTF 11kx were moving too slowly to
be coming from the recent supernova, but too quickly to be just a
stellar wind. The astronomers suspected that the star had erupted
previously, propelling shells of material outwards. The material,
they surmised, must be slowing down as it collided with a wind from a
nearby red-giant star. But for that theory to be true, the material
from the recent supernova should eventually catch up with gas and dust
from the previous nova eruptions. That is what the PTF team has
probably observed. In the weeks following the supernova, the team
watched the calcium absorption drop and eventually vanish. Then, 58
days after the supernova went off, observers at the Lick telescope
saw a sudden, strong burst of calcium emission coming from the system,
probably indicating that the new supernova material had caught up
and collided with the old shell.
It is not unusual for a star to undergo nova eruptions more than once.
Several 'recurrent novae' are known; they consist of a compact
white-dwarf star in orbit with a red giant or evolving star that is
losing mass in a stellar wind. Some of the wind material eventually
lands on the white dwarf, where it is strongly compressed by the
star's very high gravity, becomes very hot, starts to undergo nuclear
reactions, and periodically explodes. There has been some doubt as to
whether such a system could eventually give rise to a supernova, but
the recent evidence suggests that it can.
FEW GALAXIES SIMILAR TO OURS
Science Daily
Astronomers searched for groups of galaxies similar to ours in the
most detailed map of the 'local' Universe yet, the Galaxy and Mass
Assembly survey (GAMA). Simulations of how galaxies form don't
produce many examples similar to the Milky Way and its surrounds, so
they may be quite a rare occurrence. Astronomers haven't been able to
tell just how rare until now, with the discovery of not just one but
two exact matches amongst the hundreds of thousands of galaxies
surveyed. They found about 3% of galaxies similar to the Milky Way
have companion galaxies like the Magellanic Clouds. In total they
found 14 galaxy systems that are similar to ours, with two of those
being an almost exact match. Many galaxies have smaller galaxies in
orbit around them, but few have two that are as large as the
Magellanic Clouds. The research also found that although companions
like the Magellanic Clouds are rare, when they are found they are
usually near a galaxy similar to the Milky Way.
Topic: September Astronomy Bulletin (Read 1081 times)