In the show this time, we talk to Dr Chris Messenger about gravitational waves, Stuart rounds up the latest news and we find out what we can see in the February night sky from Ian Morison and John Field.
This month in the news: Hurricane Luhman.
Brown dwarfs are an unusual sort of star. During their early development they failed to accumulate enough bulk to ignite fusion in their cores resulting in them being small, dull and notoriously difficult to find or study. Thought to share more in common with gas giant planets like Jupiter or Saturn than the Sun, brown dwarfs occupy a middle ground in the cosmic zoo, which is what makes them such interesting subjects of investigation.
The atmospheres of gas giants are turbulent places. They are racked by constant storms and ferocious winds that result in the impressive bands of colour which wrap around Jupiter or form the perpetual hurricane seen by Cassini at the North pole of Saturn. So this begs the question, do brown dwarfs have extreme storms raging across their surfaces too? They are afterall effectively just super-sized gas giants. This is a question that has been wandering through the minds of astronomers since brown dwarfs were first theorised in the late 1960's. Unfortunately attempting to answer this is not an easy task since brown dwarfs are far too small to actually be resolved by a telescope and, as mentioned, even discovering them is a challenge. This is reflected by the fact only two thousand brown dwarfs have ever been discovered.
It was not until just a few years ago in 2009 that the first ever tentative hint that brown dwarfs are not just static was observed. The observations focused on one particular brown dwarf which they saw to be shifting in brightness by as much as 10% over timescales of just a few hours, the same amount of time it is expected for a brown dwarf to do a complete a full revolution. No one could be sure what was causing the shift in brightness but it was certainly considered a possibility that it was the result of thick clouds forming and shrouding the inner core of the star. Which if true would mean that brown dwarf atmospheres are at least as complex as their gas giant cousins.
Last month astronomers observing the newly discovered, and nearby, brown dwarf binary pair, Luhman 16A and B published results that seem to have confirmed finally that brown dwarfs do have stormy atmospheres. Their observations, mostly of Luhman 16B have mapped out the surface of the star revealing in detail the large dark and bright regions which they are attributing to be most likely caused by large clouds. Mapping the surface of Luhman 16B required the utilisation of a slightly abstract method that would allow the observers to overcome the problem brown dwarfs are too small and distant to be resolved by any direct observations by a telescope. The observations were made using the CRIRES spectrometer on the VLT. By using a spectrometer to observe Luhman 16B the astronomers exploited he doppler effect which allowed them to distinguish between the light from the approaching and receding edges of the star as it rotated. If the star was featureless, with no weather systems present we would expect the two sides of Luhman 16B to be equal in brightness but they were not. The astronomers measured the differences in brightness between each side of Luhman 16B and were able to build up an image of the stars surface. This technique has been used before to study brighter stars but this is the first application of it to a brown dwarf. The hope is that in the future further observations will be made which should reveal how the weather systems around Luhman 16B change over time. There is even the possibility that this technique could be used to reveal bands around the brown dwarf if higher resolution observations are made, further cementing the link between gas giants and brown dwarfs. The hope is that one day we will be able to understand, and even forecast, the weather around Luhman 16B and that such research can be applied to our models of gas giants aiding in our understanding of their atmospheres and formation.
Interview with Dr Chris Messenger
We talk to Dr Chris Messnger about detecting Gravitational Waves with LIGO. He tells us about the future prospects of advanced LIGO and the potential imminent detection of Gravitational Waves. He goes on to explain the benefit to science of such a detection.
The Night Sky
Ian Morison tells us what we can see in the northern hemisphere night sky during February 2014.
Orion the Hunter is just to the west of south in the evening, the three stars of his Belt pointing up towards Taurus the Bull, which contains the Hyades and Pleiades Clusters. Gemini lies above, with the planet Jupiter resident there this month. Following Orion's Belt downwards leads to the brightest star in the night sky, Sirius, in Canis Major. If you scan down and left from Sirius, you come to the open cluster M41, which hosts a single red giant star among its blue population. Canis Minor and its bright star, Procyon, are towards the south, while Cancer, home to the Beehive Cluster, is in the south-east. Leo the Lion is rising in the east, with its bright star, Regulus. The Realm of the Galaxies, a rich area of the sky between Leo and Virgo, rises later in the night, looking towards the Virgo Galaxy Cluster. Ursa Major, the Great Bear, is in the north-east, while Auriga and its yellow star, Capella, are above Taurus. Cassiopeia and Perseus are in the north-west, with the Milky Way running between them and the Perseus Double Cluster visible in binoculars.
- Jupiter is in the latter part of an excellent apparition. Shining at magnitude -2.6, it was at opposition (opposite the Sun in the sky) in early January. At the beginning of this month, it reaches 40° elevation by 19:00 UT (Universal Time) and over 60° by 22:00. It gets to its highest nightly elevation at around 20:30 by month's end. Jupiter is moving retrograde (westward) in Gemini, approaching the star Mebsuta. A small telescope shows the four Galilean moons and, at the right times, the Great Red Spot on the planet's surface.
- Saturn is a pre-dawn object, rising around 02:00 UT at the beginning of the month and 00:30 at the end. It lies in Libra and has a magnitude of +0.4 and a disc 17" across. The rings are 38" across and 23° from the line of sight, allowing features such as Cassini's Division to be seen with a small telescope. A larger telescope, perhaps 200mm in aperture, may allow the Enke Gap to be spotted in still atmospheric conditions. The only disadvantage is that Saturn's elevation is not very high for northern hemisphere observers.
- Mars is in Virgo, rising around 23:30 UT at the beginning of the month and around 22:30 by month's end. During February, it brightens from +0.2 to -0.5 in magnitude and grows from 9 to 11" in angular size, and its illumination of 91% allows surface features to be seen. The dark V-shape of Syrtis Major is a prominent one, while the white Northern Polar Cap may be slightly less obvious in the Martian summer. Mars progresses down through Virgo during the month, starting off 5° to the upper left of the bright blue star Spica, and ending 6° to its left as it begins moving retrograde (westward).
- Mercury reached eastern elongation (its greatest separation of 18° from the Sun in the sky) on the 31st of January. It lies 8° below a crescent Moon on the 1st of this month, with a brightness of magnitude -0.6 and an angular diameter of 7", and can be seen for up to 2 hours after sunset if you have a low western horizon. This reduces to 1.5 hours by the 7th, when the magnitude is +1, the angular size is 8" and 20% of the disc is illuminated. Mercury is quickly lost from view after this, reaching inferior conjunction (between the Sun and the Earth) on the 15th. It reappears in the pre-dawn sky at month's end, about 20° to the west of the Sun, but its very low elevation makes it difficult to spot.
- Venus passed inferior conjunction on the 11th of last month, and commences this month low in the east before dawn. Shining at magnitude -4.6, it reaches 17° elevation in the south-east at sunrise by the middle of the month, showing a crescent of 25% illumination with an angular diameter of 46". Venus concludes February 36% illuminated and 33" across.
- It is a great time to observe Jupiter in the evening this month. You can see many features through a small telescope: the North Equatorial Belt is broader than it was a few years ago, and the Great Red Spot more prominent in the South Equatorial Belt - as long as you know when to look.
- Mercury is close to a thin crescent Moon on the night of the 1st to 2nd, and the scene may be accompanied by earthshine.
- Jupiter is about 7° from a waxing Moon on the evening of the 10th.
- Mars is 5.5° above and left of the star Spica and 10° from a waning Moon before dawn on the 19th.
- The second-largest asteroid in the Asteroid Belt, Pallas, can be found for a few days around the 22nd as it approaches the 2nd-magnitude star Alphard in Hydra. It reaches opposition (opposite the Sun in the sky) on the 22nd, putting it due south around midnight. At magnitude +7, it is easily visible in binoculars - find Alphard first, and the asteroid should be in the same field of view (4° away on the 22nd). Pallas is some 550 kilometres across (although non-spherical), and on the 22nd it lies 2.1 times further from the Sun than does our own planet.
- Venus is just 0.5° above a thin, waning crescent Moon before dawn on the 26th. The pair can be seen in the south-east.
John Field from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during February 2014.
The evening sky is dominated in the north by the planet Jupiter and the constellations of Orion, Canis Major and Taurus. Jupiter, looking like a bright, white star, is in front of the distant stars that form the constellation of Gemini, the Twins. Gemini is one of the constellations through which the Sun moves as seen from the Earth; the path of the Sun across the sky is called the ecliptic, and the constellations along it form the zodiac. To the left of Gemini is an upside down 'V' of stars that forms the head of another zodiacal constellation, Taurus the Bull. The brightest of these stars is the giant, orange-hued Aldebaran, while its younger, fainter companions belong to more a distant cluster called the Hyades. Another star cluster called the Pleiades marks the Bull's back, and can be found to the west of his head. Visible as a compact cluster to the naked eye, they make a fine sight in binoculars.
Gemini and Cancer are two of the other zodiacal constellations in the summer sky. The bright stars Castor and Pollux mark the heads of the Twins, and can found in the north after sunset. Gemini lies on the eastern edge of the Milky Way, and faint and distant stars can be seen around the two main stars. Five faint galaxies can be found within 1° of Castor using a large telescope. Pollux is the brighter of the two stars. Near to the star Eta Geminorum is M35, an open star cluster. Under good conditions it can be seen with the unaided eye as a hazy star, while binoculars or a wide-field telescope present an even better view. Cancer the Crab is a fainter constellation of five stars, at the centre of which is a cluster of stars called Praesepe, or the Beehive. Large and bright, it appears as a nebula to the unaided eye, and binoculars reveal individual stars within the cluster. Galileo viewed this cluster with his telescope in 1610, becoming the first human to see it as a group of stars.
Orion the Hunter, an upside-down summer constellation in the southern hemisphere, is due north after sunset. His brightest stars, Rigel, Betelgeuse and Bellatrix, along with the three stars of his Belt, form an easily recognisable pattern. The Orion Nebula can be found in the middle of Orion's Sword, appearing as a fuzzy star to the unaided eye. Binoculars or a small telescope show a bat-shaped cloud, while a telescope of 100 millimetres or more in aperture reveals a number of stars in and around the nebula, including a tight group of four stars called the Trapezium. Above the Belt is Rigel, the brightest star in Orion, which is actually a triple system. To the east are Orion's two hunting dogs, Canis Major and Canis Minor. The brightest star in the night sky, Sirius, marks the collar of Canis Major, and the Large Dog is upside-down with his feet in the air. Below Canis Major is Procyon, forming the tail of Canis Minor, while a fainter star to the left marks the Small Dog's front. With binoculars, two lovely sights are visible: just over a third of the way between Sirius and Procyon is a cluster of stars called M50, and halfway along the line from Procyon to Betelgeuse is a rectangular cluster of stars embedded in a faint nebula called the Rosette. Almost overhead in the early evening is the second-brightest star in the night sky, Canopus.
- Mars rises in the east around midnight, and is in the constellation of Virgo.
- Saturn rises in the east some time after Mars, and lies in Libra. Like Mars, it will be better placed for viewing in the evening sky during autumn and winter.
- Venus reappears in the morning sky this month, climbing higher as the month progresses.
- Mercury also becomes visible in the pre-dawn sky towards the end of the month.
Odds and Ends
Although the Herschel Space Observatory stopped performing infrared observations in the spring of last year, scientists are still analysing the data. Last month, the European Space Observatory announced that a group led by Michael Küppers had discovered water vapour around the dwarf planet Ceres using infrared spectra from Herschel. More details can be found here.
At the end of January, something went bang in the nearby starburst galaxy M82. The culprit turned out to be a type Ia supernova, caused by a thermonuclear explosion of a white dwarf, the evolved remains of a fairly normal star. Discovered by Dr Steve Fossey and some of his students at UCL, who were carrying out an assignment on a small telescope at the time, this supernova is the closest of this type for several decades. It is now being observed by large research telescopes across the northern hemisphere, with astronomers hoping to get their closest ever view of this type of explosion.
The renowned physicist Steven Hawking has recently published an online paper (un-peer reviewed) that questions the current definition of black holes. Hawking is attempting to resolve an inconsistency between general relativity and quantum mechanics that occurs at a black hole's 'point of no return', or event horizon. Quantum mechanics calls for a big energy release at the event horizon, creating a 'firewall' of sorts, whereas according to Einstein's general relativity, the event horizon is a wholly unremarkable point in space. Hawking suggests that the event horizon is less important than the 'apparent horizon', which can change over time and eventually disappear if the black hole shrinks enough, thus re-releasing the matter it contains into the universe. It remains to be seen whether Hawking's theories will stand up to peer review.
|Interview:||Dr Chris Messenger and Chris Wallis|
|Night sky:||Ian Morison and John Field|
|Presenters:||George Bendo, Megan Argo and Indy Leclercq|
|Editors:||Sally Cooper, Indy Leclercq and Mark Purver|
|Segment Voice:||Iain McDonald|
|Website:||Sally Cooper and Stuart Lowe|
|Cover art:||The supernova in M82. CREDIT: UCL/ULO/Steve Fossey/Ben Cooke/Guy Pollack/Matthew Wilde/Thomas Wright|