In the show this time we find out about cosmology and the cosmic microwave background from Dr Hiranya Peiris and learn about buckyballs in space from Dr Jan Cami. Megan rounds up the news from the 217th AAS meeting and we hear what can be seen in the night sky in February.
The annual meetings of the American Astronomical Society are the largest gatherings of astronomers on the planet, and the presentations cover topics across the whole field of astronomy and astrophysics, including observational results, theoretical studies and simulations. Here are some of the highlights from this year's meeting.
Starting big, astronomers working on the Sloan Digital Sky Survey released the largest colour map of the sky ever made. It's freely available, but be warned - it's big! Covering a third of the sky and created from millions of 2.8 megapixel images obtained by a dedicated 2.5-m telescope over the last decade, the full image is more than a terapixel in size - that's more than one trillion pixels. But it's not just a pretty picture. The full data release, the eighth from the SDSS project, contains a catalogue of objects as well as spectra allowing astronomers anywhere in the world to use the data as the basis for a diverse range of investigations into questions of galaxy evolution, dark matter and dark energy, the distribution and motion of stars in our own Galaxy, and much, much more.
One use for sky surveys like the SDSS is searching for distant galaxies which can tell us about star and galaxy formation in the early universe. Because they are so far away, these first galaxies appear very faint by the time their light reaches us here on Earth. But there is a way around this. Gravitational lensing is the effect whereby the matter in a foreground galaxy can bend the light of a background object, making it appear distorted and magnified. This can be a helpful effect, allowing astronomers to see objects more distant than would otherwise be possible, but in surveys where the aim is to discover the size and brightness distributions of early galaxies, this effect can confuse the results. At the AAS meeting, a team of astronomers led by Stuart Wyithe at the University of Melbourne have estimated that as many as 20 per cent of the most distant galaxies currently detected appear brighter than they actually are, because of this lensing effect. With deeper surveys planned in order to probe the early universe, this lensing effect means that the best place to look for these primitive galaxies is probably near larger foreground galaxies, but understanding the lensing effects will be crucial to determining accurate statistics.
Closer to home, spiral galaxies like the Milky Way often have numerous satellite galaxies orbiting around them. Over time, these galaxies slowly spiral inwards and are eventually disrupted, becoming streams of stars that are often only detectable in large surveys. Others are just too dim to see. But Sukanya Chakrabarti, a researcher at the University of California, has developed a new method of detecting such galactic companions. These dwarf galaxies may be too small and dim to be seen directly, but their mass affects the surrounding regions of their parent galaxies, causing ripples in the clouds of hydrogen within the spiral arms. Chakrabarti's method uses these ripples to infer the mass and location of otherwise invisible dwarf galaxies and has already been used to infer the existence of an undiscovered dwarf on the opposite side of the Milky Way to the Earth. The technique has also been tested on spiral galaxies in the nearby universe where high resolution radio observations can map the hydrogen gas in detail, correctly predicting the location of the companion to the Whirlpool galaxy, M51.
Many galaxies are spirals, like our own Milky Way, containing large reservoirs of gas from which stars are currently being formed, while other so-called early-type galaxies are largely devoid of gas and no longer producing new stars. One of the current problems with our understanding of galaxy evolution is just how galaxies move from the spiral star-forming phase to the gas-poor "red and dead" phase of ellipticals. In a poster presented at the AAS meeting, a team have discovered that one particular elliptical galaxy is rapidly shedding molecular gas from its core. The galaxy, NGC1266, located in the constellation of Eridanus, is pumping out some 13 solar masses worth of molecular gas each year at speeds of up to 400 kilometres per second. Such a strong outflow could completely strip the galaxy of molecular gas required to form stars in just 100 million years, about 1 per cent of the age of the Milky Way. Many galactic outflows are driven by powerful starformation activity, but in this case there is little starformation occuring and the more likely culprit is a central black hole.
The question of which came first, galaxies, or the supermassive black holes at their cores, is an ongoing debate in astrophysics. There is a direct relation between the mass of a spiral galaxy's central bulge of stars and that of its supermassive black hole, suggesting that black holes and bulges affected each others' growth. Previous studies have found galaxies in the early universe where the black holes were more massive than this relationship would suggest, implying that black holes came first. Now, astronomers have discovered a dwarf galaxy with a central supermassive black hole but no central bulge of stars, which they say strengthens the case that black holes did come first. This dwarf galaxy has an irregular shape, and strong radio and X-ray emission characteristic of outflows from the region around a black hole, and is likely to be similar to the first galaxies which formed in the early universe.
Black holes are not all supermassive. GRS1915+105 is a binary system in the Milky Way with a black hole just 14 times the mass of the Sun, feeding on material from a companion star. As material from the companion spirals towards the black hole, it forms an X-ray emitting disk with material at its inner edge travelling at speeds of up to 50 per cent of the speed of light. Observations of the system at certain times show short pulses of X-rays being emitted every 50 seconds. Now, using a combination of observations from the Chandra X-ray Observatory and the Rossi X-ray Timing Explorer, a team think they know what's going on. In this phase, the inner region of the disk emits enough radiation to push material away from the black hole. Eventually the disk gets so bright and so hot that it disintegrates and falls towards the black hole, before the cycle begins again. Between pulses, the inner part of the disk refills from material further away from the black hole, while the radiation emitted heats up the outer disk and drives material away from the system, eventually limiting the amount of matter which the black hole can consume, and pushing the system into one of its other known states.
More well-known periodic objects are pulsars, compact remnants left over when stars larger than eight times the mass of the Sun end their lives as supernovae. One of the brightest and well-observed pulsars lies in the heart of the Crab nebula in Taurus, a pulsar which has long been thought of as one of the steadiest high energy sources in the sky. So steady, in fact, that X-ray telescopes use it as a calibrator, and the brightness of other sources are often quoted in units of "millicrabs". But now, observations made with several high energy instruments have revealed that the Crab pulsar is far less steady than has been assumed. Observations with the Gamma-ray Burst Monitor on the Fermi satellite suggested that the Crab pulsar was dimming, but to prove it was a real effect rather than an instrumental problem affecting the observations, the team made further observations with several other high energy instruments, confirming that the pulsar has dimmed by seven per cent over two years. The result has implications for the in-flight calibration of X-ray instruments, as well as possible effects on previous results where the Crab pulsar was used to calibrate the observations.
It's not just pulsars which vary. A class of stars known as Cepheid variables have a direct relationship between their maximum brightness and their period of variability. If you can measure the period, then you can calculate how bright the star would be at a given distance. By comparing this to how bright the star actually appears, you can calculate how far away it is. This relationship has long been used as a rung on the so-called cosmic distance ladder, allowing the distances of objects throughout the universe to be determined. Since Cepheids are the first rung on this ladder, and each rung on the ladder relies on the accuracy of the previous one, it is vital to much of cosmology that the calibration of Cepheid variability is accurate. But in a study carried out with the Spitzer space telescope, astronomers have discovered that the first star in the class, delta Cephei, is losing mass in a stellar wind at a rate which alters its mass and creates a surrounding nebula which affects the stars' apparent brightness. Further observations showed that as many as 25 per cent of Cepheids are also losing mass at a significant rate, with implications for distance measurements that underpin much of modern cosmology.
Even the smallest of stars turn out to be not so constant. A study of more than 215,000 red dwarf stars has found that even these old stars produce flares strong enough to disrupt the atmosphere of any orbiting planets. Originally observed in a survey to search for dimming due to transiting planets, the data were later searched for evidence of flaring and produced several interesting results. The average flare duration was 15 minutes, and some flares increased the brightness of the star by 10 per cent, making them brighter than flares on our own, much larger, Sun. The astronomers also found that variable red dwarfs were about one thousand times more likely to flare than non-variable red dwarfs, possibly due to their strong magnetic fields.
Interview with Dr Hiranya Peiris
Dr Hiranya Peiris (University College London) is a cosmologist studying the cosmic microwave background (CMB) radiation, which is the vestigial light from the time when the Universe first cooled enough to become transparent. She was previously part of the WMAP collaboration and now works on the Planck mission. In this interview, Hiranya explains what we know about the early Universe, discusses how we study the CMB and talks about being one of the subjects of Max Alexander's Explorers of the Universe project.
Interview with Dr Jan Cami
In summer 2010, Dr Jan Cami (University of Western Ontario) was the lead author on a paper reporting the detection of buckyballs in space. This discovery was reported in the August Jodcast news. In this interview, Jan tells us about the discovery and how it changes our understanding of the Universe.
Buckyballs (also known as fullerenes) are a type of carbon molecule where 60 carbon atoms are arranged in a hollow spherical structure, similar to the shell of a football (or soccer ball). They were found by Jan's team in a planetary nebula and are the largest molecules found in space so far.
The Night Sky
Ian Morison tells us what we can see in the northern hemisphere night sky during February 2011.
After sunset, Jupiter is setting in the west as Orion the Hunter towers in the southern sky. Moving upwards along Orions Belt, you reach the Hyades Cluster and the unconnected star Aldebaran in Taurus the Bull, followed by the Pleiades Cluster. The Moon is just above the Hyades on the 12th of February. The Pleiades are a haze to the naked eye, with a few stars visible in a dark sky, but binoculars or a telescope reveal many more. Beneath Orions Belt, the misty Orion Nebula lies in the middle of Orions Sword. The dust and gas of this stellar nursery is lit by the bright stars of the Trapezium at its heart. The brightest star in the night sky, Sirius, is to the lower left of the Sword, while to the upper left is the red supergiant Betelgeuse, which might be large enough to swallow Jupiter if it were in the place of our Sun. Further up and left is the constellation of Gemini, with its bright stars Castor and Pollux, the Twins, at the bottom. The open star cluster M35 is to the upper right of Castor, and the Moon will pass over it on the 14th. To the left of Gemini, the sparser constellation of Cancer the Crab contains the open cluster Praesepe, the Beehive Cluster. Hazy to the naked eye, binoculars will reveal a widely spaced group of stars. It straddles the ecliptic, so planets often appear to pass through it as seen from Earth, and on the 16th the Moon will move across it. Leo the Lion rises in the east just after, or, at the end of the month, just before, sunset; Regulus is its brightest star. Ursa Major, the Great Bear, is in the northern sky as usual. Its bright asterism, the Plough, has an apparent double star as the middle of its handle, resolvable with binoculars or even the naked eye. With a telescope, you can see that the brighter of the two is itself a double star.
- Jupiter is low in the west after sunset, and will disappear as an evening object during March. Its South Equatorial Belt continues to re-emerge after disappearing last year, while the Great Red Spot is still more prominent than usual. The planet is easily visible to the naked eye at magnitude -2.2, and a telescope will reveal the Galilean moons around it: Io, Europa, Ganymede and Callisto. Jupiter is close to the crescent Moon on the 6th and 7th of the month.
- Saturn rises earlier in the evening as the months progresses, appearing around 22:30 at the beginning and 21:00 GMT at the end. Its brightness gradually increases from +0.6 during the month as its rings turn increasingly away from edge-on as seen from Earth, reaching 10°. A small telescope now allows the Cassini Division, the gap between Saturns A and B rings, to be made out. Its brightest moon, Titan, can be observed through binoculars.
- Mercury and Mars pass behind the Sun (superior conjunction) on the 25th and 4th of the month respectively.
- Venus is prominent in the pre-dawn sky. It rises slightly later through the month while the Sun rises earlier, but still gets high enough in the southern sky to be visible before sunrise. Its angular size decreases from 19 to 16 as it moves away from Earth during the month, but the illuminated portion of its surface increases from 61 to 71%, so its magnitude drops by only 0.1 magnitudes.
- The asteroid 7 Iris is near the 5th magnitude star 8 Cancri on the 5th, and is visible using binoculars in a dark sky or more easily through a telescope. Making two observations, a few hours apart, you should be able
- Also on the 5th, three of Saturns moons form a triangle on its eastern side. Dione, Rhea and Tethys are all around 10th magnitude, so a telescope is needed to see them below and left of the brighter moon Titan.
- The 14th is a good time to observe the lunar craters Tycho and Copernicus using binoculars or a telescope. Tycho is in the Southern Lunar Highlands near the bottom of the Moon, and is relatively young at 108 millions years old. It may have been formed by the impact of one of asteroids of the Baptistina Family, which originated in the breakup of a single object. Another of the Family could have been responsible for creating the Chicxulub Crater in Mexico 65 million years ago. Tycho is 85km wide and 5km deep, and is surrounded by arc-like trails produced by the collision. Copernicus is more ancient, at around 800 million years old, and lies in the Oceanus Procellarum towards the left side of the Moon, just beyond the end of the Apennine Mountains. It is 93km wide and 4km deep, with terraced edges.
- The 5th magnitude star 81 Geminorum is occulted by the dark limb of the Moon at 01:30 GMT (Greenwich Mean Time) on the 16th>, causing it seemingly to disappear just to the upper left of the Moon. This should be visible with binoculars, but difficult for the naked eye.
- Venus is close to the crescent Moon before dawn on the 28th, and closer still a day later.
John Field from the Carter Observatory in New Zealand speaks about the southern night sky during February 2011.
This month sees Jupiter slip lower into our twilight sky, leaving us bereft of planets until Saturn rises in the east around midnight at the start of the month. Orion is almost due north after sunset and will slide towards the western horizon as the month progresses. Taurus, along with the Pleiades or Matariki, will be lower in the west and will set by midnight. The eastern sky is bereft of bright stars until the rising of Scorpius, nearer dawn, after midnight.
Last month we toured some of the sights near Gemini; this month we visit the fainter constellations of Cancer, Leo and Virgo. Cancer appears as a square of stars with the faint star cluster called Praesepe (the Manger). It is more commonly called the Beehive Cluster. The Beehive Cluster is best seen through binoculars or a wide-field telescope at low power when over 40 stars may be visible. The cluster has a similar age and motion to the Hyades Cluster, the V-shape forming the head of Taurus. This implies that they may have formed out of the same cloud of dust and gas.
Being far from the plane of the Milky Way, the following zodiac constellations of Leo and Virgo are prime targets for galaxy hunters. Leo rises in the evening followed by Virgo around midnight. Galaxies come in a variety of shapes, sizes and brightnesses. The two brightest in our southern hemisphere skies are the Large and Small Magellanic Clouds. These appear as two hazy, cloud-like, patches that are circumpolar from New Zealand. Both are irregular in shape and are about 10% and 5% of the mass of our galaxy respectively. They are both around 170,000 to 200,000 light-years distant. A more challenging galaxy is Centaurus A, which is 4° north of the globular cluster Omega Centauri in the constellation of Centaurus. It can be seen in binoculars as a haze with a dark band running across it. This band has given rise to its nickname of the Hamburger Galaxy. The brightest galaxy visible in the northern hemisphere sky is the Andromeda Galaxy. It is visible low on our northern horizon during our spring here in the southern hemisphere. Andromeda is estimated to be similar in mass to our Milky Way galaxy and around 2.5 million light-years away. The galaxies in Leo and Virgo are much more distant and many times fainter than the other galaxies mentioned. But many are within the range of binoculars and small telescopes on a moonless night well away from city lights. Leo appears as an upside-down sickle in our night sky with the bright star Denebola marking the lions tail. Leo contains many bright galaxies, Messiers 65 and 66 along with 95 and 96. Messier 105 and NGC 3628 form part of the Leo Triplet of galaxies. Rising after Leo is Virgo, the second-largest constellation in the night sky. Virgo is marked by the bright star Spica and a faint, but easily seen, rectangle of stars. A much brighter object in Virgo is the planet Saturn, appearing as a yellow star that is similar in brightness to Spica. The Virgo Cluster is a group of up to 2000 galaxies whose center is about 54 million light-years away. It is the part of the larger Local supercluster, of which the galaxy is an outlying member. One of the brighter galaxies in this cluster is the giant elliptical galaxy M87. At Magnitude 9.5, this galaxy is a good target for small telescopes, appearing as a small haze.
Venus and Mercury are in the morning sky with Venus high up below Antares in Scorpious. Mercury is in the morning twilight sky rising about an hour sunrise, but it will move closer to the Sun and by mid-month will be lost in the Suns glare.
Odds and Ends
Recently there have been stories and rumours circulating that Betelgeuse is set for an imminent supernova. Betelgeuse is a red supergiant star, easily spotted as the top-right corner star in the constellation Orion. The star has a mass of about 20 times that of the Sun, so that it will eventually end its life in a supernova, leaving a neutron star remnant. If we're lucky this neutron star will manifest itself as a pulsar, and we will observe it from Jodrell Bank. As discussed during the show, when Betelgeuse does explode we can expect its brightness to reach a visual magnitude comparable to the Moon. What is untrue, although it has been suggested by some, is that it will be as bright as the Sun. Nor will it take up a large patch of the sky - it will just be a very bright star. It has even been claimed that Betelgeuse is guaranteed to go supernova in the next year, when in fact it may not happen for 100,000 years or more! So if somebody tells you that Betelgeuse is exploding any day now, and that it will turn night into day, and we will have a "second sun" then take it with a pinch of salt. When they start explaining how it is linked to Mayan prophecies of the end of the world you should already have left the room.
NASA's first solar sail, NanoSail-D successfully deployed on January 20. NASA and Spaceweather.com have partnered up to run a photo competition to find the best images of NanoSail-D while it remains in orbit. The competition runs until the solar sail re-enters Earth's atmosphere in April or May 2011. Some of the best photos are featured on the NASA Marshall Space Flight Centre Flickr group.
Libby has been to Taiwan recently and got a couple of JodPics at Taipai 101 and the Chiang Kai-shek memorial hall in Taipei. If you have a Jodcast t-shirt and go somewhere interesting, don't forget to take a photo of yourself there in your t-shirt and send it in!
|Interview:||Dr Hiranya Peiris, Jen Gupta and Mark Purver|
|Interview:||Dr Jan Cami and Jen Gupta|
|Night sky:||Ian Morison and John Field|
|Presenters:||Jen Gupta and Evan Keane|
|Editors:||Jen Gupta, Megan Argo, Claire Bretherton and Mark Purver|
|Intro/outro:||Dara O Briain|
|Segment voice:||Lizette Ramirez|
|Website:||Stuart Lowe, Jen Gupta and Mark Purver|
|Cover art:||Artist's conception of buckyballs coming from a planetary nebula Credit: NASA/JPL-Caltech|
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