In the news this month: neutron stars, the cosmic web and a black hole.
Neutron stars are without a doubt some of the most extreme objects known to astronomers. They are formed when a massive star runs out of fuel to sustain the nuclear fusion processes that push back against gravity. The star effectively collapses under its own weight, and if its mass is in the right region (roughly 8-30 solar masses), it will compress down to a neutron star. The density in a neutron star is around 10^12 kg/cm3, meaning that a teaspoonful of the stuff would weigh roughly as much as every human being alive (around a 400 million tons). They also rotate extremely quickly, tens or even hundreds of times a second, and possess a magnetic field up to a trillion times that of the Earth. Magnetars are a subset of neutron stars which rotate at a slower pace (about once every few seconds) and with a magnetic field thousands of times stronger than a regular neutron star - these objects have the strongest fields in the known universe!So far, only 20-odd magnetars have been detected. One of them has recently been behaving unexpectedly, though: astronomers using the X-Ray telescope SWIFT have found that its rate of rotation abruptly slowed down. While neutron stars have been observed to sporadically speed up their rotation for short periods of time (known as a 'glitch'), this is the first time a star has slowed down like this, a phenomenon that has been dubbed an 'anti-glitch'. While the mechanisms involved are not fully understood, it is thought that interactions between the star's fluid, inner components and its outer crust made of iron are responsible. These may rotate at different rates: if the crust slows down slightly, the superfluid neutron interior will remain spinning at the same speed. but from time to time it, too, will slow down, and by conservation of momentum the surface will speed up, thus explaining a glitch. Complex magnetic effects, moving material around the crust and the inner fluid may be responsible for the opposite effect, with the inner fluid slowdown and subsequent speedup causing the anti-glitch. The observation of this anti-glitch is in any case going to help increase our understanding of the truly exotic objects that are neutron stars.
Since the coining of the term 'Island Universe' by Immanuel Kant to describe the nebulae people suspected were distinct entities, the study of galaxies has come a long way. While the image is poetic, we now know that galaxies are not isolated in space; the predominant theory behind galaxy formation is that of hierarchical growth: small clumps of matter interact gravitationally, colliding and merging with each other to form bigger and bigger objects, and eventually galaxies. Simulations of this mechanism have been quite successful in describing the formation of elliptical galaxies. However observational evidence has shown that big, bright galaxies are more commonly found when looking back to earlier times in the universe - this goes against the model of large galaxies building over time. Furthermore, it has been calculated that at the rate galaxies are using up their hydrogen to form new stars, they should run out in a few billion years - but galaxies such as our own Milky Way have been steadily consuming hydrogen for more than 13 billion years.It is in fact possible that the galaxies are even more linked than we thought: numerical simulations have suggested that galaxies consist of only around 1/3 of the so-called baryonic, or ordinary matter: protons, electrons and neutrons. The other two thirds are supposedly to be found in intergalactic filaments of gas, forming a sort of cosmic web. This would be where all the hydrogen the galaxies are consuming is coming from. Furthermore, it seems that the gradual condensation of these giant clouds is more responsible for the formation of galaxies than the hierarchical interaction model. Why hasn't this model been suggested sooner? Until recently, the huge intergalactic filaments were incredibly difficult to spot - they're mainly formed of ionized hydrogen, a hydrogen atom that has lost its electron. Direct detections are extremely fiddly, but since intergalactic hydrogen is never 100% ionized, it is possible to pick up some neutral hydrogen and infer the presence of its ionized counterpart. This is exactly what a team of astronomers has done, mapping the so called 'fractional neutral hydrogen' located between the Andromeda and Triangulum galaxies. This was a very challenging task: the fractional hydrogen is 10 000 times less dense than the hydrogen commonly observed in galaxies, and the detection was made at the limits of current technology. Nevertheless, this opens the door for more direct studies of the intergalactic gas, which will greatly help our understanding of galaxy formation and evolution processes, and of how they interact with their surrounding medium.
Finally, astronomers have observed some surprisingly hot gas in the neighbourhood of Sagittarius A*, the bright radio source that is theorized to be the location of the Milky Way's central, supermassive black hole. Like most other spiral and elliptical galaxies, our own galaxy contains a huge black hole at its centre. The origin of these central singularities is still the subject of much research and debate, although observations at very high redshift (thus looking back towards the early universe) show that black holes could be in place at the centres of galaxies as early as 1 billion years after the big bang. Our own black hole has a mass of about 4 million times that of the sun and is located around 26,000 light years away from the solar system. A team of astronomers using the Herschel space observatory found clouds of extremely hot gas (around 1000 degrees Celsius, much hotter than the usual handful of degrees above zero) less than a light year away from the black hole. Herschel is an infrared telescope, which can see through the dust obscuring the centre of the galaxy and reveal the environment around the black hole.It is suspected that the high temperatures of the gas are due to shocks and collisions within the gas caused by strong magnetic fields.
Interview with Prof. David Neufeld
Prof. David Neufeld from Johns Hopkins University, USA, talks to us about hydrides, discussing what they are and how we can observe them using both Herschel and SOFIA, an airborne infrared observatory. He discusses hydrogen fluoride (HF) specifically and talks about its uses in deriving abundances of molecular hydrogen. He also goes on to tell us about SH, also known as a mercapto radical, why it was absent from previous interstellar observations and what it can tell us.
The Night Sky
Ian Morison tells us what we can see in the northern hemisphere night sky during June 2013.
Leo the Lion is in the west after sunset. Between Leo's hindmost star, Denebola, and the bright star Arcturus, in Boötes, is the constellation of Coma Berenices, which hosts part of the Virgo Galaxy Cluster. Corona Borealis, the Northern Crown, is an arclet of stars near between Boötes and Hercules. The four brightest stars in Hercules make a trapezium shape called the Keystone, and the globular cluster M13 can be found two thirds of the way up one side of it. The bright star Vega, in Lyra, is towards the east, and near to it is the Double Double - Epsilon Lyrae - which appears as a double star in binoculars but as a pair of double stars through a telescope. Cygnus the swan rises high into the sky later in the night, with its bright star Deneb. Altair, in Aquila, is lower to the south-east and completes the Summer Triangle of Vega, Deneb and Altair. About a third of the way from Altair to Vega is the dark region of the Milky Way called the Cygnus Rift, as well as the asterism called Brocchi's Cluster or the Coathanger.
- Jupiter is still just about visible at twilight at the beginning of the month. It shines at magnitude -1.8, but is lost against the setting Sun by mid-month, after which it will re-emerge into the pre-dawn sky towards the end of July.
- Saturn is in Virgo and crosses the south as darkness falls. It is near the first-magnitude star Spica, but appears more yellow in colour. Its angular diameter decreases from 18.5 to 17.8" over the month as it moves away from us. It also approaches the star Kappa Virginis, which has a magnitude of +4.2, and is 0.5° away from it at month's end. Saturn's rings are now at 17° to the line of sight, allowing the largest gap between the rings, Cassini's Division, and the planet's largest moon, Titan, to be seen using a small telescope. Saturn's maximum elevation each night is now quite low, and will continue to decrease over the coming years.
- Mercury forms the top of a line with Venus and Jupiter on the 1st. It has a magnitude of -0.4, and reaches greatest eastern elongation (its furthest easterly point from the Sun in the sky) on the 12th. It is best seen at that time, being 24° from the Sun, and can be most easily viewed around 30 minutes after sunset. A telescope will show its slightly gibbous disc, 8" across. Mercury is 2.1° from Venus on the 18th, moving below it to 1.9° separation the following night. You made need binoculars to locate Mercury at this time, so be sure to use them only after the Sun has gone down.
- Mars reached superior conjunction (passing behind the Sun) on the 18th of April, and this month appears in the eastern sky before dawn. It rises about 30 minutes before the Sun on the 1st. It is difficult to spot at magnitude +1.4, but this becomes easier by the end of the month, when it is 7° above the horizon shortly before dawn. You may still need binoculars to find it, so put them away before the Sun comes up.
- Venus is about 8° above the western horizon 30 minutes after sunset at the beginning of the month. It does not get very high in the sky, reaching 10° elevation around the 20th-25th. Its disc, 10" across, is 96% illuminated at the star of June as it is on the far side of the Sun, shining at magnitude -3.8. By the end of the month, it is still 91% illuminated.
- The asteroid Ceres can be found between the 5th and 7th, when it passes within 1° of the star Pollux, in Gemini. Look towards the west about an hour after sunset using binoculars to spot the asteroid at magnitude +8.8, but don't mistake it for a star of magnitude +8.4 nearby!
- Mercury, Venus and a thin crescent Moon congregate on the 10th, visible shortly after sunset if you have a low western horizon. You may also spot earthshine - sunlight reflected from the Earth and reflected again from the dark part of the Moon.
- A gibbous Moon appears very close to Spica, in Virgo, on the 18th, with Saturn not far away.
John Field from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during June 2013.
The south-eastern evening sky is dominated by the zodiacal constellations of Scorpius the Scorpion and Sagittarius the Archer. The red star Antares marks the Heart of the Scorpion, and its name means 'The Rival of Mars'. To Māori, and some Polynesians, Scorpius is seen as a fishing hook. Rehua is one Māori name for Antares, showing the blood of Māui staining the eye of the Hook. Straddling the Milky Way, the region around Scorpius is home to a number of nebulae and star clusters. The globular clusters M4 and NGC 6144 are near to Antares and can be observed using binoculars, while a number of double stars can be found along the body of the Scorpion. The open star cluster NGC 6231 appears rather like a comet to the naked eye and is near to the Scorpion's stinger, as is the hazier-looking open cluster M7. M6, the Butterfly Cluster, is in the same region but is fainter. Sagittarius also contains a wealth of nebulae and star clusters, while its brightest stars form the asterism known as the Teapot. Using binoculars, the globular cluster M22 can be found near to Lambda Sagitarii, which marks the top of the Teapot. M8 and M20 - otherwise known as the Lagoon Nebula and the Trifid Nebula - make spectacular sights in Sagittarius. M8 is a compact open cluster surrounded by a circle of nebulosity containing a dark rift. M20 is similar, but is distinguished by dark lanes that split the nebula into three segments. The constellation of the Archer also hosts M23, an open cluster forming arcs of stars, M24, a looser cloud of stars, M25, an open cluster containing several deep yellow stars, and M55, a globular cluster. The Milky Way is at its brightest, widest and densest around Scorpius and Sagittarius because we are looking towards the centre of our Galaxy, some 30,000 light-years away. In Arabic it is Al Nahr, the river, to the Chinese it is the River of Heaven, and to Māori it is Te Ika Roa, the Long Fish. It contains dark bands consisting of gas and dust which may eventually form new clusters of stars.
The planet Saturn is easily spotted in the northern sky after sunset, while Venus appears with Mercury in the west. The Moon will also be in the west as the Sun sets on the 10th, while Venus and Mercury will be only 2° apart on the 20th. The 21st marks the winter solstice, when the Sun rises and sets at its most northerly points and the night hours are at their longest. This date was celebrated in many cultures. In Aotearoa (New Zealand), the dawn rising of Matariki (the Pleiades Cluster) and Puanga (the star Rigel) coincide with the winter solstice, and mark the beginning of the new calendar year in the Māori system known as Te Maramataka.
Odds and Ends
The International Space Station welcomed three new crewmembers on the 29th of May. Russian Fyodor Yurchikin, American Karen Nyberg and Italian Luca Parmitano formed Expedition 36 and joined the three astronauts already on board to complete the crew. Parmitano is the first of ESA's new batch of astronauts to go up to the ISS. The spacefarers have a busy schedule ahead, with over 70 hours of experiments a week to conduct.
Seats on a Virgin Galactic space flight with a "mystery guest" were auctioned at the Cannes film festival auction for the amfAR Cinema Against AIDS charity. The mystery guest is reported to be Leonardo DiCaprio and the seat next to him sold for 1.2 million Euros. A second pair of seats on the same flight sold for 1.8 million Euros. The 'normal' price for seats on a Virgin Galactic space flight is $250,000 and around 550 people have already paid for (either partially or fully) tickets. Commercial flights could happen as early as 2014.
Late in May, the European Space Agency (ESA) collected ideas from astronomers for the next two large (or L-class) ESA missions. ESA only plans to fund three of these L-class missions in the next two decades. Last year, ESA selected the JUpiter ICy moons Explorer (JUICE) as its first L-class mission in this time period; the spacecraft is scheduled to be launched in 2022. The next two missions, which will be selected over the course of the next few years, would be scheduled for launch in 2028 and 2032. ESA could select from a variety of mission concepts, including a mission ot other planets, asteroids, or comets; a spacecraft that can be used to measure gravitational waves from binary pulsars and merging black holes; a new X-ray space telescope, a new infrared/millimetre all-sky survey telescope; or a high-resolution infrared telescope. More information on the selection process as well as ESA's Cosmic Visions program can be found here .
|Interview:||Christina Smith and David Neufeld|
|Night sky:||Ian Morison and John Field|
|Presenters:||George Bendo, Indy Leclercq and Christina Smith|
|Editors:||Adam Avison, George Bendo, Claire Bretherton, Indy Leclercq and Mark Purver|
|Segment Voice:||Mike Peel|
|Website:||Indy Leclercq and Stuart Lowe|
|Cover art:||The Galactic centre, seen here in infrared from the 2MASS project. Obscured by dust clouds in viible light, the galactic centre is home to a plethora of stars and a supermassive black hole around 4 million times as massive as the Sun. CREDIT: Atlas Image [or Atlas Image mosaic] obtained as part of the Two Micron All Sky Survey (2MASS), a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.|