In our sixth birthday show, we talk to Professor Chris Collins about galaxy formation and we find out about molecules in space from Dr Serena Viti. Megan rounds up the latest news and we hear what we can see in the January night sky from Ian Morison and John Field.
In the news this month:
Black holes come in various sizes. Some, the result of stellar explosions, have masses of a few times that of the Sun, but these are tiny compared to those that sit in the centres of galaxies. Such galactic black holes often have masses of several million times that of the Sun. The largest one known until now, with a mass of 6.3 billion solar masses, was that in the centre of the giant elliptical galaxy M87. And, while the observed characteristics of quasars in the early Universe suggest that at least some of these extremely luminous objects were powered by black holes of more than 10 billion solar masses, no remnants of such monsters have been found in the local Universe. Now, a US-Canadian team has discovered not just one, but two central black holes with masses far exceeding that of the the black hole in M87.
The team, led by Nicholas McConnell of the University of California, used the Gemini North and Keck 2 telescopes in Hawaii to observe two relatively nearby massive elliptical galaxies. To measure the masses of the central black holes, the team used devices known as integral-field spectrographs, detectors which can record spectra at several points on the sky simultaneously. By looking at the spectra from the cores of these galaxies, the astronomers could determine the speed of the stars around the black hole from the shift in the colour caused by the Doppler effect - the faster a star moves, the greater the colour shift. The speed of an object in orbit is determined by the mass of stuff inside that orbit, so measuring the motions of the stars and modelling the velocity distributions enabled the astronomers to calculate the masses of the black holes in these two galaxies. In most galaxies however, such a measurement is difficult, if not impossible, so other indirect methods of estimating black hole masses have to be used.
Both of the galaxies observed in this study, NGC 3842 and NGC 4889 are of a type known as brightest cluster galaxies, or BCGs, so-called because they are giant elliptical galaxies located near the centre of thier home clusters. NGC4889 is the brightest galaxy in the Coma cluster, located some 103 megaparsecs from the Milky Way. Since larger galaxies tend to host heavier black holes, such galaxies are good places to look in the search for extremely massive black holes. So far, only 65 galaxies have had their black hole masses measured directly, and only four of those have been BCGs like the two galaxies in this study, so very little is known about the properties of extremely massive black holes and how they relate to their host galaxies. The observations, published in Nature on December 8th, showed that the black holes at the centre of both NGC 3842 and NGC 4889 are extremely massive, the most massive black holes so far found in the local Universe, with that in NGC 3842 having a mass of 9.7 billion solar masses and that in NGC 4889 having a comparable, possibly slightly larger, mass.
These new results show that extremely massive black holes, such as those thought to have existed in the early Universe, do still exist today. The study also has implications for galaxy evolution models. There is a widely-used relation between black hole mass and the range of speeds of stars in a given galaxy (a quantity known as the stellar velocity dispersion), but these new discoveries show that, for black holes with very large masses, the relationship breaks down, suggesting a different evolutionary process for such galaxies.
The closest supermassive black hole to the Solar System is the one sitting in the middle of the Milky Way. Located in the middle of our Galaxy's central bulge, this particular black hole, known as Sagittarius A-star (SgrA*), has a mass of only four million times that of the Sun. Unlike black holes in many other galaxies, SgrA* is currently quiet. Compared to other supermassive black holes thought to be about the same size, ours is very faint, suggesting that the rate of accretion of material from the surrounding environment is currently very low. But now, a team of astronomers has detected a cloud of gas on an orbit which will take it extremely close to the black hole.
Because it is so much closer to us, directly measuring the mass of SgrA* is far easier than for supermassive black holes in other galaxies. Since 1992, a team of astronomers has been observing SgrA* and its surrounding stars regularly. Using images taken with the Very Large Telescope in Chile, the researchers have been following the motions of individual stars in orbit around the black hole, allowing them to make a direct measurement of its mass. In the December 15th issue of Nature, they report that during the course of their observations they have discovered a cloud of gas which is on an orbit which will take it into the accretion zone of the black hole.
The cloud has a mass of roughly three times that of the Earth and will pass the black hole at a distance of just 36 light hours (3100 times the size of the event horizon), an event which we will see sometime in the summer of 2013. Since 1992, only two stars have been observed to pass so close to the black hole. Observations of the cloud over the last three years show that it has already begun to break up. It is currently moving towards the black hole at 1,700 km/s, and a combination of pressure from the surrounding (less dense) gas, together with gravitational shear caused by the black hole itself, will create instabilities which will disrupt the cloud, causing it to disintigrate as it travels towards the black hole.
The researchers predict that as shocks cause the cloud to disrupt, its temperature should increase to more than one million degrees, causing X-ray emission. If the cloud fragments, then the X-ray emission should vary as shock fronts pass through different parts of the cloud. The team also suggests that, as the cloud passes the black hole along its highly elliptical orbit, some of the gas may collide with other parts of the cloud, pushing it into a circular orbit from where it will be likely to accrete onto the black hole. Since little is known about the detailed physics of black hole accretion, observations across the electromagnetic spectrum during the next decade will provide astronomers with a unique laboratory for testing our understanding of the process.
And finally: December 16th saw Comet Lovejoy fly through the Sun's atmosphere and later emerge intact, something many thought was impossible. Comets are composed of a compact core of dirt and ice, leaving a dusty tail of debris behind in their orbital paths. Comet Lovejoy was discovered by Terry Lovejoy on December 2nd 2011, and was quickly found to be a member of the Kreutz family of sungrazing comets. Such sungrazing comets are numerous and typically very small, but Lovejoy is some ten times larger than usual, estimated to be around 200 metres in diameter. The orbit of the comet was predicted to take it through the Sun's hot atmosphere, passing just 120,000 km above the stellar surface. Many observers expected that, because of the comet's size, it would not survive the encounter, but images from telescopes such as the orbiting SOHO and the twin STEREO spacecraft quickly showed that the comet had in fact survived intact. As the comet continued on its orbit moving away from the Sun, it began to regrow its tail of debris, resulting in quite a spectacle in the early morning sky. The fact that the comet survived its encounter with the Sun suggests that it was significantly larger than 200 metres in size before passing through the corona, possibly as large as 500 metres. The comet continues to put on an impressive show as it moves away from the Sun, but the possibility remains that the encounter significantly weakened the nucleus and it could still break up completely.
Interview with Prof. Chris Collins
Melanie talks to Prof. Chris Collins from Liverpool John Moores University, who discusses testing galaxy formation models using the most massive galaxies. These models are mostly based on how structure in the Universe forms, and use massive particles and gravitational perturbations and, in the more complicated cases, gas dynamics. The evolution of structure is then followed through cosmic time. Using XMM-Newton X-ray observations of galaxy clusters, Prof. Collins discusses discrepancies between what is expected from the models and what is actually observed in the Universe.
Interview with Dr Serena Viti
George interviews Dr Serena Viti from University College London, who talks about her interests in molecules in space and how they can be used to understand everything from protostars to interstellar magnetic fields to very distant galaxies.
The Night Sky
Ian Morison tells us what we can see in the northern hemisphere night sky during January 2012.
There is a lovely sky to start the new year off with. Orion the Hunter is due south in the evening. The three stars of his Belt point down and to the left towards the bright star Sirius in Canis Major. Up to the right we come to Taurus the Bull and the little group of stars called the Hyades, which has an interloper, Aldebaran, a bright orange star that forms the eye of Taurus. Carrying on beyond, we come to the group of stars called the Pleiades, an obvious target for a small telescope. Looking at the two bright stars in the centre of Pleiades, one has a triplet of fainter stars beside it and between it and the other there's a double star, one of which is nice and red. Starting with the central star of Orion's Belt, drop down to the Sword where there is the Orion Nebula, a region of star formation. At its heart is a group of four or five very blue stars called the Trapezium. Up to the left of Orion we have Gemini, with Castor above and Pollux below. Down below them is Procyon, the bright star in Canis Minor. Above Orion is Auriga, coming up towards the zenith, with its bright yellowish star called Capella. The Milky Way runs between Orion and Gemini, above Taurus and through Auriga. There are some very nice little star clusters - M36, M37 and M38 - which can be picked out with binoculars and are nice to observe with a telescope. As the evening goes on, Leo the Lion rises in the south east.
- Jupiter is beautiful in the evening sky. On January 1st, at 7.30pm, it will be at about 50° elevation due south, on the boundary of Pisces and Aries. Its angular size is about 41". The equatorial bands are still easily visible, with the Great Red Spot in the Lower Belt and dark markings called 'barges' currently visible in the North Equatorial Belt.
- Saturn is in the pre-dawn sky. On January 1st it rises at 2am, and by 5am it is about 28° above the horizon. The rings are about 15° from the line of sight, so Cassini's Division can be seen with a small telescope. Its angular size is 17".
- Mercury is also in the pre-dawn sky, towards the south-east, brightening from magnitude -0.4 at the beginning of the month to -0.7 by the end. Its angular size decreases down to 4.8" by the end of the month.
- Mars rises before midnight and before dawn it is about 47° high, due south. It increases in brightness to magnitude -0.4 by month's end, and its angular size increases to 11". It is now possible to see details on the salmon-pink disk, such as the V-shape of Syrtis Major and the North Polar Cap.
- Venus is now gradually increasing its separation from the Sun and reaches 34° away. Its elevation at sunset is about 18°. Its angular size is increasing but the the surface illumination is decreasing, so its magnitude stays constant at -4 throughout the month.
- Early morning on January 3rd/4th is the Quadrantid meteor shower. The radiant is between Boötes and the handle of the Plough. There can be up to 200 meteors per hour, but they are not very bright and visibility is hampered by a first-quarter Moon in the sky. The Moon sets at 3.30am, so from 1-2am its light should not be too much of a problem.
- Looking south west on January 10th, Asteroid Vesta is about 3' up to the left of the star Tau Aquarii in Aquarius. It is at magnitude +8, so binoculars should pick it out.
- On January 12th/13th/14th, Neptune is just above and to the right of Venus, shining at magnitude +8. On January 13th, use binoculars to centre Venus in the field of view and Neptune should be up and to the right, about a third of the way to the edge of the field of view.
- There is a nice skyscape on January 16th, about an hour before dawn, with Saturn close to a third-quarter Moon and Spica, the brightest star in Virgo.
- On January 26th, just after sunset, at about 4.40pm, there is a chance to spot Venus and a thin crescent Moon. It should be possible to see Earthshine, or "the old Moon in the new Moon's arms".
John Field from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during January 2012.
January finds the planets Venus and Jupiter in the evening sky. Venus is low down in the west, setting about two hours after sunset. Jupiter is higher in the north and will set around midnight. In early January, Jupiter moves from the constellation of Pisces the Fish into the constellation of Aries the Ram. Aries is a faint constellation containing a number of double stars, but larger telescopes are needed to easily observe them.
In sharp contrast to faint Aries, Orion the Hunter has a large number of bright stars and sights for binoculars and any size of telescope. Orion's brightest stars, Rigel, Betelgeuse and Bellatrix - along with the three stars of his Belt - form an easily seen pattern in the evening sky. Well placed for viewing is the Orion Nebula, which can be found in the middle of Orion's Sword. To the unaided eye, this nebula appears to be a fuzzy star. If you have binoculars or a small telescope, you will see a bat-shaped cloud. A telescope with an aperture of 100mm or more will reveal a number of stars in and around the nebula, including a tight group of four stars called the Trapezium. Marking Orion's left foot is Rigel, the brightest star in Orion, shining at magnitude +0.18.
Running from a star nearby to Rigel and across the sky to Achernar is the long and rambling constellation of Eridanus, the River. Epsilon Eridani is a magnitude +3.7 dwarf star. Theta Eridani (Acamar) is a pair of blue-white stars of magnitudes +3.2 and +4.4, separated by just over 8", that are easily seen through a telescope. 32 Eridani is a beautiful double star for small telescopes, consisting of a magnitude +5 yellow star and a blue-green magnitude +6.3 companion separated by just under 7". 40 Eridani is a remarkable triple star system: small telescopes will reveal a magnitude +4.4 yellow star; nearby is a widely separated magnitude +9.6 white dwarf companion, the most easily seen white dwarf star in the sky. Large telescopes will show that the white dwarf has an 11th magnitude red dwarf companion. Also along the river is NGC 1535, a small planetary nebula appearing in a nice field of scattered stars.
Returning to the northern sky, we find Taurus, along with the Pleiades (Matariki to the Māori) to the west of Orion, which sets around midnight. To the east of Orion are his two hunting companions Canis Major, the Larger Dog, and Canis Minor, the Smaller Dog. The brightest star in our night sky, Sirius, marks the collar of Canis Major.
For those staying out later, Mars rises after midnight in the constellation of Leo. It appears as a reddish coloured star and is brighter than any of the other nearby stars. Later, Saturn will rise in Virgo, its rings slowly tilting towards us, which will lead to better views of them later this year.
We have a visitor to the inner Solar System that may be visible in early January. Comet Lovejoy made a close approach to the Sun on December 15th 2011, and by late December it was visible throughout the night in the south. This comet may now have dropped in brightness as it moves away from the Sun, and might only be visible through telescopes.
Odds and Ends
The Russian Mars probe, Phobos-Grunt (supposed to land on Phobos, collect rock samples and return them), which got stuck in Earth's orbit in November after failing to fire its engines, is going to fall to back to Earth. The probe's mass when it was launched was 13 tonnes and experts expect most of the probe to burn up upon re-entry. However, approximately 200kg are expected to make it to the surface in 20-30 pieces and it is likely that these will end up in the ocean. The date of re-entry is not well known, but is expected to be around January 9th, plus or minus 5.5 days - but some forecasters are predicting re-entry as early as January 1st.
NASA has announced that SpaceX will attempt to dock an unmanned Dragon Capsule with the International Space Station in February. The launch date has been set for February 7th, and will mark the first launch of an American spacecraft to the ISS since the retirement of the space shuttles in July 2011.
The newest telescope to be built at the European Southern Observatory's Paranal Observatory in Chile, the VLT Survey Telescope, has captured a spectacularly detailed wide-field image of the nearby galaxy NGC 253. This galaxy is one of the closest examples of a starburst galaxy: a galaxy going through a period of very rapid star formation. It's well worth having a play with the "zoomable version" of the image to see the galaxy up close.
Further media attention centred on two more Earth-sized exoplanets discovered by the Kepler mission. Once again, they are not entirely Earth-like. A number of exoplanet apps are available which notify the owner of new discoveries via their mobile phone, and even give information about the properties of each planet.
|Interview:||Prof. Chris Collins and Melanie Gendre|
|Interview:||Dr Serena Viti and George Bendo|
|Night sky:||Ian Morison and John Field|
|Presenters:||Megan Argo, David Ault, Jen Gupta, Libby Jones, Mark Purver and Christina Smith|
|Editors:||Mark Purver, Claire Bretherton, Melanie Gendre, Jen Gupta and Dan Thornton|
|Segment Voice:||Kerry Hebden|
|Website:||Mark Purver and Stuart Lowe|
|Cover art:||An image of nearby starburst galaxy NGC 253 from ESO's new VLT Survey Telescope at Paranal Observatory, Chile. CREDIT:: ESO/INAF-VST/A. Grado/L. Limatola/INAF-Capodimonte Observatory|