DISTANT PLANET HAS CARBON DIOXIDE ETC
ESA
Scientists using the Hubble telescope have discovered carbon dioxide
and carbon monoxide, methane and water vapour in the atmosphere of a
Jupiter-size planet 63 light-years away.
DIMMEST STARS YET FOUND
NASA/Jet Propulsion Laboratory
Brown dwarfs are objects with masses between those of planets and of
stars; they are not massive enough to ignite the nuclear fires that
power normal stars. The first incontrovertible one was found only in
1995, and astronomers are still finding progressively fainter
examples. A new record has been claimed for the dimmest known
star-like object, by a supposed pair of brown dwarfs. Previously,
astronomers thought the pair of stars was just one typical, faint
brown dwarf, but they have recently concluded that it must be a binary
system although it has not been seen as such. It is called 2MASS
J09393548-2448279 after its entry in the Two-Micron All-Sky Survey.
Data from the Spitzer infrared space telescope indicated atmospheric
temperatures of 565 to 635 Kelvin. While that is hundreds of degrees
hotter than Jupiter, it is still very cold as far as stars go.
In fact the object is the coldest star-like one measured so far.
To calculate its intrinsic brightness (candle-power), the researchers
had first to determine its distance. From measurements made at the
Anglo-Australian Observatory in Australia, they concluded that it is
the fifth-closest known brown dwarf to us; it is 17 light-years away,
towards the constellation Antlia. That distance, together with
Spitzer's measurements, showed that the object was both cool and
extremely dim. The brightness was, however, actually twice what would
be expected for a brown dwarf with that particular temperature.
Therefore (the argument runs) it must have twice the surface area; in
other words, it must be twins, with each body shining only half as
bright, and each with a mass of 30 to 40 times that of Jupiter. Both
bodies are a million times fainter than the Sun in total luminosity,
and at least a billion times fainter in visible light alone.
STUDY TRACKS STARS ORBITING MILKY WAY BLACK HOLE
ESO
In a 16-year study made with several ESO telescopes, a team of
astronomers has produced the most detailed view yet of the
surroundings of the super-massive black hole at the centre of our
Galaxy. The research has mapped the orbits of 28 stars, many more
than previous studies. One of the stars has now completed a full
orbit around the black hole known as Sagittarius A* (spoken as
"Sagittarius A-star").
The astronomers observed at infrared wavelengths that penetrate the
dust that blocks the Galactic Centre from view in visible light. They
regarded the central stars as 'test particles' and watched how they
moved around Sagittarius A*. In comparison with previous studies, the
new work improved the accuracy with which the positions of the stars
were measured by a factor of six. The final precision was 300 micro-
seconds of arc. The observations could be used to infer the mass of
the black hole itself, and its distance. They also showed that at
least 95% of the mass sensed by the stars has to be in the black hole
-- so there is comparatively little scope left for other dark matter.
The stellar orbits in the Galactic Centre show that the central mass
concentration of four million solar masses must be a black hole,
almost beyond doubt. The observations also allowed the astronomers to
determine with some precision our distance, 27,000 light-years, from
the centre of the Galaxy.
One particular star, known as S2, orbits the Milky Way's centre so
fast that it completed a full revolution within the 16-year period of
the study. Observing the complete orbit of S2 made a crucial
contribution to the high accuracy reached. It is not understood,
however, how the stars came to be in the orbits in which they are
observed to be today. They are much too young to have migrated far
from their birthplaces, but it seems even more improbable that they
could have formed in their current orbits where the tidal forces of
the black hole must be expected to prevent any gas cloud from
condensing into stars.
DISTANT WATER
NRAO
Astronomers using the 100-m radio telescope in Effelsberg, Germany,
and the Very Large Array (VLA) in New Mexico have detected the radio
spectral lines of water molecules in a galaxy more than 11 billion
light-years away, much further away than water had been seen before.
The galaxy, MG J0414+0534, has a quasar -- a super-massive black hole
powering bright emission -- at its core. In the region near the core,
the water molecules are acting as masers, the radio equivalent of
lasers, to amplify radio waves at a specific frequency. The
astronomers are quoted as saying that their discovery indicates that
such giant water masers were more common in the early Universe than
they are today, although it is hard to see how such a sweeping
generalisation could validly be made from just a single example.
MG J0414+0534 is seen as it was when the Universe was roughly
one-sixth of its current age.
At the galaxy's great distance, even the strengthening of the radio
waves by the masers would not by itself have made them strong enough
to detect with the radio telescopes. However, the scientists had help
from nature in the form of another galaxy, nearly 8 billion light-
years away, located directly in the line of sight to MG J0414+0534.
That intervening galaxy's gravity serves as a lens to brighten the
more-distant galaxy. The gravitational lens produces not one, but
four, images of MG J0414+0534 as seen from here. Using the VLA, the
scientists found the specific frequency attributable to the water
masers in the two brightest of the four images (the other two are
still too faint). The radio frequency emitted by the water molecules
was Doppler-shifted by the expansion of the Universe from 22.2 GHz to
6.1 GHz.
Water masers have been found in numerous nearer galaxies. Typically,
they are thought to arise in discs of molecules closely orbiting
super-massive black holes at the galaxies' cores. The amplified radio
emission is more often observed when the orbiting disc is seen nearly
edge-on. However, MG J0414+0534 seems to be oriented almost face-on
to us, so the water molecules that we are seeing may not be in the
disc; they might be in jets of material being ejected from the
vicinity of the black hole.
Topic: January Astronomy News (Read 960 times)