March 2011: Llama

In the show this time we find out about quasars from Dr Alejo Martinez-Sansigre, and Dr Alastair Edge tells us about the gas between clusters of galaxies. Megan rounds up the latest news and we hear what we can see in the March night sky from Ian Morison and John Field.

The News

• Normal massive galaxies contain supermassive black holes in their central bulges. Observations have shown evidence for such objects in pretty much all massive Milky Way-like galaxies, as well as large elliptical galaxies. But not all galaxies are as large as the Milky Way. Many dwarf galaxies are known in the nearby universe, usually irregular in shape and often forming stars much faster than galaxies like our own. Now, a team of astronomers, led by Amy Reines at the University of Virginia, have found evidence for a supermassive black hole in the centre of one of these dwarf irregular galaxies. The galaxy, known as Henize 2-10, is a small galaxy located some 30 million light years away in the southern constellation of Pyxis. It is classified as a blue compact dwarf and is highly irregular in shape. Despite being similar in mass to the Large Magellanic Cloud, Henize 2-10 is forming stars some ten times faster. The team observed the galaxy with a number of telescopes operating in different parts of the electromagnetic spectrum as part of a survey of several galaxies. When they looked at data taken with the Very Large Array, a collection of radio telescopes situated in New Mexico in the USA, they found a small object at the centre of the galaxy which was very bright at radio wavelengths. When they looked with the Hubble Space Telescope they found that the object was not a large cluster of stars, several of which exist in other parts of Henize 2-10, but data from the archive of the Chandra X-ray telescope showed that there was a source of X-rays at the same position. The amount of energy being emitted by this object in different parts of the spectrum is consistent with it being a supermassive black hole with a mass estimated to be roughly two million times that of the Sun. This is an exciting but unexpected result, since few dwarf galaxies are known to contain supermassive black holes, and those that do are forming stars far more slowly than Henize 2-10, and there is evidence that the black hole is growing by actively consuming material from the surrounding galaxy. This discovery has implications for our understanding of the growth of galaxies in the early universe, since the properties of Henize 2-10 (it's active black hole and simultaneous rapid star formation) resemble those of low-mass high-redshift galaxies seen in the distant universe when the early stages of galaxy assembly and evolution were happening on a large scale.

• While the planet Mars is home to the largest volcano in the solar system, and the enormous Mariner Valley which cuts through a huge region of the planet's surface, the crust of the planet is today fairly inactive. Unlike the Earth, where plate tectonics cause the continents to move and ever-so-slowly collide with each other, Mars today has no such large-scale geological activity. But that doesn't mean the surface never changes with time. Several spacecraft have been imaging the surface of the red planet over many years, some at very high resolution, and the images sent back are showing an amazing amount of surface change on short timescales. In 2010, images released from the High-Resolution Imaging Science Experiment on the Mars Reconnaissance Orbiter showed evidence of avalanches on sand dunes first imaged by Mariner 9 in the 1970s located in the northern polar region. Most older images of the region suggested that it was mostly stable with very little variation over time, but last year's images from the MRO show clear evidence of sediment transport with one image even catching a dust cloud kicked up by an avalanche. Now, a team led by Candice Hansen at the Planetary Science Institute in Arizona in the USA, have analysed the images and determined the cause of the avalanches. The team found that numerous dunes in the northern polar region showed evidence of morphological changes over the course of a Martian year. Seasonal variations have been seen in images from previous Martian orbiters, but this is the first time they have been seen in such detail that the underlying processes can be studied. Some of the physical processes causing the changes are the same as those seen on sand dunes here on the Earth, but on Mars there is an additional process not found on the Earth. The Earth's polar caps are made of ice, but the atmosphere of Mars has a very high percentage of carbon dioxide, a gas which freezes in the cold temperatures of the Martian winter and settles on the surface. In the Martian spring, the carbon dioxide ice sublimates, turning back into a gas and returning to the atmosphere. This sublimation process can destabilise the dunes, especially at the top where more sunlight is received and the side of the dune is steepest, causing loosened sand to cascade down the side of the dunes, creating gullies and aprons of material. Over the area studied, a dune field 6.4- by 19.2-km in size, roughly twenty per cent of the dunes showed measurable changes over one Martian year and another twenty per cent showed slight changes. The widespread nature of these variations and the pristine appearance of the dunes suggests that sand transport on the surface is an active and ongoing process. Similar image comparisons of dunes at lower latitudes further from the polar regions show no changes in dune shape over the same period, adding to the evidence that the observed changes at high latitude require carbon dioxide ice.

• And finally: After a prolonged period of very little activity, the Sun produced the first X-class flare of solar cycle 24 during February. X-class flares are the most powerful solar events, producing X-rays and sending large amounts of charged particles out into space in what is known as a coronal mass ejection, or CME. Originating from a spot on the Sun's surface known as Active Region 1158, a region wider than Jupiter containing several sunspots, this particular eruption (the strongest in four years) peaked at 0156 UT on February 15th and resulted in a CME heading in our direction, producing some good displays of aurora at high latitudes a few days later. On February 18th, sunspot complex 1161-1162 also erupted, sending a further significant CME in the Earth's direction. Now that the Sun's activity is starting to increase again, it is worth taking a look, but make sure that if you do observe the Sun, you do it safely. NEVER point a telescope or binoculars at the Sun.

Interview with Dr Alejo Martinez-Sansigre

Dr Alejo Martinez-Sansigre (Institute of Cosmology and Gravitation at the University of Portsmouth) tells us about quasars, the most luminous objects in the universe. In this interview, Alejo explains exactly what a quasar is and why they are more common in the early universe.

Interview with Dr Alastair Edge

Dr Alastair Edge (Durham University) is an extragalactic astronomer researching the gas between clusters of galaxies from an X-ray perspective. In this interview, Alastair explains how this hot gas made its way into the intracluster medium, and discusses how ALMA can be used to detect and study this gas and its role in active galactic nuclei feedback.

The Night Sky

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during March 2011.

Constellations such as Orion and Taurus become visible as the Sun sets, but are themselves beginning to set in the west. Other constellations are more easily seen now, such as Gemini, the Twins. Gemini is up and to the left of Orion, in the south-west in the mid-evening. Its two main stars are Castor and Pollux. Looking to the feet of the uppermost twin, which has Castor at its head, the open cluster M35 can be seen to the right using binoculars. Moving east, Cancer, the Crab, lies in a relatively empty patch of sky. At its heart is the wide open cluster M44, known as the Beehive Cluster or Praesepe. Continuing in the same direction leads to the Sickle, an asterism forming the head of the constellation of Leo, the Lion. Its brightest star is Regulus, or Alpha Leonis, part of its front knees. Denebola marks the Lion's tail. Moving horizontally from Regulus, a small telescope allows a number of galaxies to be seen: M95, M96 and, further over, M65 and M66. Virgo rises to the lower left of Leo in the evening, with its brightest star Spica, or Alpha Virginis. Between Leo and Virgo, beneath the small constellation of Coma Berenices, lies the "Realm of the Galaxies", which is in the direction of the Virgo Cluster. Comprising over 1000 galaxies, this cluster is home to a number of the galaxies in the Messier Catalogue, which are visible through a small telescope in a clear sky. Ursa Major, the Great Bear, makes its best appearance at this time of year, high overhead. Within this is the asterism of the Plough, or Big Dipper (named after the soup ladle used on farms in North America). The line between the rightmost two stars of the Plough, from Merak up to Dubhe, points towards Polaris, the Pole Star or Northern Star. Alcor and Mizar are in the centre of the Plough's handle, a multiple star system that can just be discerned as two objects with the naked eye. A small telescope shows that Mizar is itself a double star, and a redder companion star can also be seen.

The Planets

• Jupiter is coming to the end of its current apparition (period of visibility), and can be seen low in the west after sunset. It has a magnitude of -2.1 and an angular diameter of 33.5", and its surface features and moons can be seen through a small telescope. By the end of the month, Jupiter is obscured by the Sun.
• Saturn is now becoming an evening object as it approaches the best part of its current apparition. The time at which it rises moves back from around 21:00 UT (Universal Time, almost identical to Greenwich Mean Time) to about 20:00 BST (British Summer Time, one hour ahead of GMT) during the month. It is at its highest point and due south at around 03:00 GMT at the beginning of the month and about 01:00 BST by the end. It has a magnitude of +0.5, which is brighter than a year ago as its rings have opened out from our point of view. They reached 10° from edge-on earlier in the year, but the motion of the Earth has brought them down to about 9° this month. The rings are 42" in diameter, and the dark Cassini Division between the A and B rings can now be made out.
• Mercury is at its best this month. It is seen well in the spring evenings because of the steep angle between ecliptic and horizon, which puts it quite high in the sky despite its proximity to the Sun. It begins the month at a magnitude of -1.4, and moves away from the Sun during March, decreasing in brightness as it does so. By the time of its greatest eastern elongation (maximum angular separation from the Sun) on the 23rd, it has a magnitude of +0.4 but is fairly high in the sky.
• Mars is hidden behind the Sun.
• Venus shines in the pre-dawn sky at a magnitude of -4.1. It rises an hour before the Sun, at 05:30 GMT. The shallow angle between ecliptic and horizon in the mornings means it doesn't get very high in the sky, despite its large angular distance from the Sun. Its angular size drops from 15.4 to 13.7" during the month, while its fractional illumination increases as it begins to move to the far side of the Sun, keeping its brightness roughly constant. Venus is almost lost in the Sun's glare by month's end.

Highlights

• Mercury is 5° to the left of a very thin crescent Moon in the west at sunset on the 5th.
• Jupiter and a thin crescent Moon lie about 9° above Mercury on the 6th.
• Jupiter and Mercury are just 2° apart on the 15th in the early evening, putting them in the same field of view in binoculars or a small telescope.
• Jupiter is a little way below Mercury on the western horizon after sunset on the 23rd.
• The dark limb of the Moon occults the 3rd magnitude star Eta Geminorum at 21:07 GMT on the 13th in the mid-UK (time varies slightly with location), causing it to apparently wink out of existence. It reappears from behind the bright limb of the Moon an hour later.
• Saturn's moons can be seen through a telescope when the Moon is not nearby in the sky. The brightest is 8th-magnitude Titan, while Dione, Rhea and Tethys are also visible in a clear sky. On the 1st and 2nd, they cluster close to Saturn in a Moonless sky, with Titan to the right. The free computer programme Stellarium shows where these moons will be at any given time
• A feature on the Moon known as the Straight Wall can be observed through a telescope just after first quarter or just before third quarter, which are on the 13th and 25th respectively. This reasonably straight and relatively gentle scarp appears as a dark shadow or a bright line, depending on its angle of illumination by the Sun.

Southern Hemisphere

John Field from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during March 2011.

March sees our summer constellations of Taurus, Orion and Gemini sliding towards the western sky a little more each night. Our nights are quickly becoming longer and this means the opportunity for more observing! In the west the Pleiades/Matariki set earlier each evening and will soon be lost in the twilight, returning, in our morning sky, at the time of our winter solstice. One version of the Waka of Tamarereti has the Pleiades forming the carved prow of a Māori canoe, the 'V' of stars in Taurus forming the sail and Orion's Belt and Sword forming the stern and carved stern-post of the canoe. This was the canoe in which Tamarereti sailed across the heavens placing Nga Whetu - the stars - across the heavens. The 'V'-shaped head of Taurus consists of the more distant Hyades Cluster, which contains the half-sisters of the Pleiades, along with the much closer and brighter star Aldeberan, which forms one of the Bull's eyes. The name Aldebaran originates from the Arabic for "the follower", as this star follows the Pleiades across the sky. Aldebaran has a distinct orange hue and is a K5 type star that is 65 light years away and 150 times brighter than the Sun. It has used up the hydrogen fuel in its core and is now fusing hydrogen in a shell around the core. The star's radius has increased to 44 times that of the Sun, and as a result has a cooler surface temperature of around 4000 degrees Celsius. The spectral type of a star is based on its spectral lines and temperatures. Today they fall into the following sequence: O,B,A,F,G,K, M (going from hottest to coolest). The moniker "Oh Be A Fine Guy/Girl Kiss Me" is often used to remember it.

Sirius, the brightest star in the sky, is an A type star, while our Sun is a G type and Proxima Centauri, the closest star to our Solar System, is a faint M type red dwarf. Aldebaran is slightly variable in brightness, but the change is imperceptible to the human eye. It is also one of the few very bright stars that can be occulted (hidden) by the Moon. One of these events was observed from Athens in 509, and during his tenure in the 1700s Astronomer Royal Edmond Halley realised that Alderbaran could not have remained in the same position for this to have happened. This meant that Alderbaran must have moved over the intervening 1200 years by one quarter the diameter of the Moon. Halley went onto discover that a number of other stars had also moved in their positions over recorded history. This shifting of star positions is due to the fact that all the stars, including the Sun, are moving in their orbits around the Galaxy. The nearby stars show the greatest amount of angular movement. Every 50 years, updated star atlas are released to account for this motion. From our Solar System, we see, over many millennia, the shifting of the stars. The constellations we see today will look very different in one hundred thousand or a million years time.

The Hyades Cluster is about 150 light years distant and consists of at least 130 stars brighter than 9th magnitude. It also contains a number of double, or multiple, stars. It has used up or lost the interstellar material from which it formed, and now travels as a loose open cluster that is estimated to be 700 million years old. Almost due north is the zodiacal constellation of Cancer, the Crab, which appears as four stars with the Beehive Cluster at the centre. Rising up in the eastern evening sky is the planet Saturn, appearing as a bright yellow 'star' in the constellation of Virgo. Through a telescope, the rings will appear as a thin disc around the planet as the rings are almost edge-on to us.

In the southern sky, the Cross and the star Achernar appear opposite each other and about halfway up the sky. The midway point between the two marks the South Celestial Pole. A third of the way back from Achernar we find the two Magellanic Clouds, two dwarf galaxies orbiting the Milky Way. There are 14 known dwarf galaxies that orbit our Galaxy. It is thought that suc galaxies are formed during the birth of their parent galaxy or following interactions with other large galaxies. The tidal forces in these interactions stimulate the collapse of material in the halo of galaxy and this leads to dwarf galaxies forming. One of the local dwarf galaxies is located in the constellation of Canis Major, about 25000 light years from our Solar System. It is being torn apart by the gravitational pull of the Milky Way. Recent studies of the globular clusters M79, NGC 1851 and NGC 2808 suggest they may have been 'stolen' from this dwarf galaxy. Another disrupted dwarf galaxy was discovered by a team led by New Zealander Mary Williams. This galaxy is in the direction of the constellation of Aquarius. The region with the greatest number of globular clusters is the Scorpius/Sagittarius region which rises after midnight.

For those up in the early morning, the planet Venus rises in the east around 04:00 NZDT (New Zealand Daylight Time) in New Zealand. On the 1st of March the crescent Moon is close to Venus. Mercury, Mars and Jupiter are too close to the Sun to be observed.

Odds and Ends

Recently there has been speculation from two scientists from the University of Louisiana about the existence of a ninth planet called Tyche in the far reaches of our solar system, on the outer edge of the Oort Cloud. According to John Matese and Daniel Whitmire, the presence of a planet with up to four times the mass of Jupiter, would explain the odd behaviour of some comets in that region. Whilst the planet has yet to be observed, it is believed that evidence for its existence could be found by the NASA space telescope, WISE, which will release its data some time in April.

The Stardust spacecraft successfully flew by Comet Tempel-1 in early February 2011, and researchers are extremely pleased with the results. The mission principle investigator was even quoted saying that it was "1000 percent successful!". The comet had previously been imaged by the Deep Impact spacecraft in 2005, which also flung a probe into the nucleus. This time, scientists have been to observe the resulting impact crater and learn about the composition of the comet. Other scientific goals included identifying changes since Tempel-1 looped around the Sun, imaging areas not previously seen before, and analysing the dust and debris surrounding the comet.

With the ramping up of solar activity towards the solar maximum in 2013 there will be an increase in solar flares and coronal mass ejections caused by the sudden release of magnetic energy stored in the Sun's atmosphere. The waves of charged particles interact with the Earth's magnetic field and could result in the northern lights (Aurora Borealis) being visible in northern parts of the UK. Space Physicists at Lancaster University have set up email alerts and a twitter account @aurorawatchuk to keep you updated on when the aurora may be visible from the UK.

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