… to a new home at Scientific American.
And it has a new RSS feed: http://rss.sciam.com/basic-space/feed. Don’t forget to update your RSS reader!
First of all, an apology. This blog has been very quiet of late — I’ve been writing up my thesis and taking my final exams. But as of last Friday all that is finished and am now the proud owner of a (provisional) upper second class degree in physics from Imperial! I have also managed to move house, which you’ll realise is no mean feat if you know how much of a hoarder I am.
Now to the exciting news. As of today this blog will have a new home on the brand new Scientific American Blog Network! Click here to go and read my introduction post now. I am really excited about the move and I hope you will head over there to check it out.
There are a lot of really amazing bloggers joining the network and I’m honoured to have my blog amongst theirs. So go and read Bora’s introduction to the network or Editor-in-Chief of Scientific American Mariette DiChristina’s welcome post and make yourself at home over there.
It may look like a static yellow ball from here, but in reality the Sun is alive with activity. Right now it is becoming more active each day as we get closer to the next solar maximum, which is expected to peak in July 2013. However, a couple of years ago it was quieter than it had been for nearly a century. It had very few sunspots and radiated very little energy. This variation is normal — the Sun goes through regular cycles where its activity and number of sunspots go up and then down again. What was unusual was the depth of this solar minimum.
Dibyendu Nandy, from the Indian Institute of Science Education and Research in West Bengal, and colleagues Andres Munoz-Jaramillo and Petrus Martens, from Montana State University, think they might have found the reason for this almost unprecedented solar calm.
Each solar cycle lasts roughly 11 years. After this time, its magnetic field flips over. After two cycles the magnetic field has flipped twice and it ends up back where it started. During these cycles the amount of solar activity goes up and down too.
Sunspots are a good measure of the amount of activity going on in the Sun at any point, and the number of sunspots on the Sun follow the 11 year solar cycles; there are more sunspots at a solar maximum and less at a minimum. A sunspot’s magnetic field is very strong and stops the transfer of heat from the interior of the Sun to the surface. Sunspots look dark because this loss of heat makes them cooler than their surroundings. In fact the surrounding area is brighter than it would be without the sunspot. This means that, counterintuitively, the more sunspots there are on the Sun, the more energy radiates out of it — even though it looks darker than usual.
The last solar minimum was unusual because there were a very high number of days — about 800 — without any sunspots at all. Nandy and colleagues created a computer model to try to work out why this happened.
They found that great loops of electrical current, which flow in the plasma that makes up the Sun, were interfering with the formation of new sunspots. In a plasma, the electrons have been stripped away from their atoms, leaving them free to move about and conduct such currents. The currents flow around the surface of the Sun, going down into the interior at the poles and resurfacing at the equator. Dying sunspots get dragged underneath the surface, where their magnetic field is given a boost. They are then sent back up to the top to form a new sunspot.
During a deep solar minimum, however, it doesn’t quite happen like this. In the first half of the solar cycle the plasma flows quickly, but in the second half it slows down. This fast movement at the start stops strong magnetic fields forming inside the Sun, so that it eventually runs out of steam and stops making sunspots during that cycle. The slow plasma flow afterwards means that the formation of the next lot of sunspots takes a bit longer to get going that usual.
This all adds up to long stretches of time without a single spot on the surface of the Sun.
The team’s simulation, which modelled this physics, reproduced what we saw during the last solar minimum, showing that very deep solar minima are generally linked to the Sun’s weakened magnetic field.
Being able to predict when solar minima like this are going to occur is a very useful thing. When the Sun’s magnetic field is weakened, so is the solar wind. The solar wind is a stream of charged particles that are ejected from the Sun’s atmosphere and into space, and is responsible for aurorae, geomagnetic storms and the tails of comets, amongst other things. It also stops lots of cosmic rays getting into the solar system. When the Sun’s magnetic field is weakened, the solar wind lets more cosmic rays through, making space a more dangerous place. This new model will hopefully mean we can predict hazardous changes in space weather and plan missions accordingly.
Nandy D, Muñoz-Jaramillo A, & Martens PC (2011). The unusual minimum of sunspot cycle 23 caused by meridional plasma flow variations. Nature, 471 (7336), 80-2 PMID: 21368827
Sunspot plotter — find the number of sunspots on any day back to Jan 1st 1755
You might not be able to tell from wherever you are reading this, but black holes in the distant universe just shrunk down to as little as a tenth of their previous size. This is not some cosmic disappearing act; a new analysis of supermassive black holes at the centres of active galactic nuclei has revealed that their masses were previously overestimated by up to a factor of ten. The paper was published in Nature last week.
Active galactic nuclei, or AGN, are among the most luminous objects in the universe and are powered by massive black holes millions of times the mass of the Sun. Gas clouds, known as “broad line regions” for reasons that will become clear later, surround the black holes. These gas clouds range from a few light days to hundreds of light days across; they are much wider than our solar system. Astronomers have been studying these clouds for over thirty years, but had not worked out the why some of them were flatter than others — until now.
Wolfram Kollatschny and Matthias Zetzl from the Institute for Astrophysics, at the University of Göttingen in Germany, looked into the relationship between the shape and width of spectral lines observed in the emission spectra of AGN. An emission spectrum is produced when an object, a gas cloud for example, blocks a light source, such as a star. The light coming the source gets absorbed into the gas cloud, and is eventually re-emitted. Astronomers can measure the intensity and wavelengths of the light that gets re-emitted. Spectral lines are spikes in the emission spectrum, and represent a lot of light at a certain wavelength. They can tell astronomers what elements are present in the gas cloud.
However, for the gas clouds surrounding black holes, it is not quite that simple. The regions are spinning very fast around the central black hole, and the light emitted from them is subject to the Doppler effect. The Doppler shift is seen, or rather heard, in more everyday situations too — when the pitch of an ambulance siren seems to rise as it speeds towards you in the street and fall as it gets further away. That’s the Doppler shift affecting the sound waves. It happens because the ambulance is moving as it emits the sound waves, so the frequency of the waves _appears_ to change.* When gas rotates around a black hole, the same thing is happening to the light rays because some of the gas is moving away from the observer quickly and some is moving towards the observer quickly. This makes the spectral line astronomers eventually observe broader — an effect known as Doppler broadening. This is the reason the gas clouds are called “broad line regions”.
Kollatschny and Zetzl looked at 37 active galactic nuclei. They worked out that fast rotating AGN created broader spectral lines, and slower ones made more narrow lines. From their observations, they saw that faster rotating AGN had flatter gas clouds surrounding them, and slower ones had more rounded gas clouds. As they now knew how fast AGN were spinning, they were also able to come up with new, more accurate estimates of the masses of their central black holes. Previous estimates used just the spectral lines to estimate masses. This is a problem, particularly for very distant AGN, as astronomers can usually only see one spectral line from these — so there’s nothing else to check any estimated against.
The new black holes masses came out between two and ten times smaller than the previous estimates. While this isn’t going to cause any major problems for the black holes themselves — they’re still the most massive objects in the universe — it may pose a problem for astronomers studying the formation of black holes.
*Wikipedia has a good animation illustrating the Doppler Effect.
Kollatschny, W., & Zetzl, M. (2011). Broad-line active galactic nuclei rotate faster than narrow-line ones Nature, 470 (7334), 366-368 DOI: 10.1038/nature09761
Galaxy clusters are some of the largest structures in the universe. Astronomers have found these clusters, which are large groups of galaxies bound together by gravity, as far back as only 4 billion years after the Big Bang (less than a third of the age of the universe). They know they contain stars that formed even earlier than that. But nobody had caught a cluster while it was still forming — until now.
Astronomers have found a “protocluster” that was around only 1 billion years after the Big Bang (that’s a redshift of 5.3 for anyone that’s counting). It sits in a region that is 40 million light years across and is rich in young stars.
The protocluster was found in data from the Cosmological Evolution Survey, COSMOS. COSMOS uses the Hubble, Spitzer and Chandra space telescopes with the ground based Keck Observatory and Japan’s Subaru Telescope to get an good look at the universe. COSMOS looks at a tiny region of space — about 0.005% of the whole sky, or two square degrees — in all wavelengths of light, from radio to gamma waves.
Peter Capak, the lead author on the paper published in Nature last week, and colleagues knew that extremely bright objects such as starburst galaxies (galaxies with an unusually high amount of star formation) and quasars (the bit at the centre of a massive galaxy that surrounds the supermassive black hole) should exist in very young galaxy clusters, so they first looked for objects giving off a lot of radiation. They found objects emitting a lot of visible light by measuring optical and near-infrared radiation, starburst galaxies by taking radio wave measurements and quasars using X-rays. Once they had located these extreme objects, they looked in the areas surrounding them for unusually large numbers of galaxies given the size of the area — something they called “overdensities”. They then used Hubble and Subaru to measure how far away these extreme objects were, and the Keck II telescope in Hawaii to confirm the observations.
Capak and colleagues were particularly interested in an “overdensity” near a starburst galaxy known as COSMOS AzTEC-3. The area in question contained over 50 billion times the mass of the Sun in gas (and ten times more dark matter), and was brighter than 10 trillion Suns. Stars in the region are forming at a rate of over 1500 a year, more than a hundred times the average value.
Around COSMOS AzTEC-3 there were 11 bright galaxies — 10 more than would normally be expected. This led to the conclusion that what they were seeing was the beginnings of a galaxy cluster, known as a protocluster.
Chandra X-ray observations helped to pin down a quasar very close to the protocluster. It can be difficult to find quasars that are this far away because, although they are the most luminous objects in the universe, they’re not usually bright enough to be seen by the telescope. But this one was. The astronomers worked out that the quasar’s black hole must have a mass of between ten and a hundred million times the mass of the Sun.
Putting all of this information together, astronomers worked out the total mass of the protocluster. It weighs in at at least ten billion time the mass of the Sun, but could be up to a hundred billion Suns. This confirmed what the astronomers suspected: they were looking at one of the biggest and brightest objects at this distance.
Astronomers also measured the amount of gas in the protocluster. This is what will fuel the protocluster’s growth. They found more than enough to point to a very bright, and massive, future for the baby cluster. It will eventually evolve (or rather, confusingly, already has evolved — depending on which way you look at it) into a massive galaxy cluster. Massive clusters of galaxies have been found from around 4 billion years after the Big Bang, giving this one at least 3 billion years to grow up.
Capak PL, Riechers D, Scoville NZ, Carilli C, Cox P, Neri R, Robertson B, Salvato M, Schinnerer E, Yan L, Wilson GW, Yun M, Civano F, Elvis M, Karim A, Mobasher B, & Staguhn JG (2011). A massive protocluster of galaxies at a redshift of z ≈ 5.3. Nature, 470 (7333), 233-5 PMID: 21228776
It’s also on arXiv.
Last November I wrote about the most distant galaxy ever seen. Since then, one even further away has been found. This post is (slightly) adapted from an article I wrote for Felix about this new galaxy.
There haven’t always been stars and galaxies in the universe, and the time when they began to form — known as the reionisation epoch — is the subject of much interest in astrophysics. A paper published in Nature details a discovery that could tell us more about this mysterious time.
In the paper, Rychard Bouwens and colleagues say they have detected the most distant galaxy ever seen; the light from the galaxy was emitted only 500 million years after the Big Bang. This age puts it well within the epoch of reionisation.
The galaxy has the highest redshift ever observed; it was from this that the team were able to calculate the galaxy’s age.
Cosmological redshift is a measure of how fast an object is moving away from the Earth and is a consequence of the expanding Universe. Objects with higher redshift are moving away from the Earth faster than those with lower redshifts, which means they are further away from Earth and also further back in time. To put it simply, the higher the redshift the older the galaxy.
Bouwens and colleagues used something known as the Lyman-break technique to identify the galaxy. This technique relies on a sharp drop in the spectrum of a galaxy that is due to the absorption of energetic photons by neutral gas that surrounds galaxy forming regions. The discovery can then be confirmed by looking at optical images.
For a long time the observations required to study the reionisation epoch were out of reach, but recent images from Hubble are making the detection and study of far away galaxies possible for the first time. The new galaxy was discovered in images taken by Hubble’s Wide Field Camera 3.
Bouwens and colleagues also looked into the rate of star formation at the time just after the newly discovered galaxy. They discovered that in just 200 million years the rate of star formation increased tenfold. This confirms that the newly discovered galaxy is right in the heart of the reionisation epoch, and sheds new light on how the stars and galaxies we see today formed.
It seems that galaxies around at the same time as this new discovery may not have been able to fully reionise the universe. This leaves the means by which the universe went from being a neutral gas to an ionised one, with electrons and protons stripped away from each other, a mystery. However, the existence of galaxies at this time does point to the first stars forming 100 million years beforehand, or around 400 million years after the Big Bang.
“We’re seeing huge changes in the rate of star birth that tell us that if we go a little further back in time we’re going to see even more dramatic changes,” said Garth Illingworth, a co-author of the paper from the University of California at Santa Cruz. “We’re moving into a regime where there are big changes afoot. Another couple of hundred million years back towards the Big Bang, and that will be the time when the first galaxies really are starting to build up.”
Bouwens, R., Illingworth, G., Labbe, I., Oesch, P., Trenti, M., Carollo, C., van Dokkum, P., Franx, M., Stiavelli, M., González, V., Magee, D., & Bradley, L. (2011). A candidate redshift z ≈ 10 galaxy and rapid changes in that population at an age of 500 Myr Nature, 469 (7331), 504-507 DOI: 10.1038/nature09717
Last week astronomers working on the European Space Agency’s Planck experiment convened in Paris to talk about their first results, and they weren’t short of things to say. No less than 25 papers were announced on Tuesday 11th January — and this is before work has even started on the mission’s main aim of putting together a detailed picture of the Cosmic Microwave Background, or CMB.
The CMB is a uniform glow of microwave radiation, with only tiny fluctuations, that gives us a snapshot of the universe around 380,000 years after the Big Bang. We’ve seen it before, courtesy of WMAP in 2003 and COBE in 1992. But Planck has the power to look at this faint glow in never-before-seen detail, revealing more about the universe than every before.
Video showing locations of the different compact objects found by Planck.
Before they can get to work on this new view of the CMB, however, astronomers must study the foreground noise of the picture in detail. This “noise” is made up of structures formed after the CMB: galaxies, galaxy clusters, and matter within the Milky Way, such as gas and dust.
Planck astronomers studied this “noise” in order to better understand how they can remove it from the picture, and just see the CMB. It’s called noise because it gets in the way when we try to look at the CMB, but actually it’s very interesting in its own right. These structures can tell us a lot about the formation of stars, galaxy clusters and even the universe itself — and that’s what some of the 25 new papers announced last week are about.
First up, we have galaxy clusters. They’re the largest structures in the universe, and the Planck mission has just completed the first all-sky survey of them using something called the Sunyaev-Zel’dovich effect (SZE). Galaxy clusters don’t just contain galaxies; they also hold hot gas and a large amount of dark matter. The SZE arrises when high energy particles in the hot gas interact with the CMB and distort it. Astronomers can see this distortion in the CMB and use it to detect galaxy clusters.
In total, 189 galaxy clusters have been detected by Planck using the SZE. This includes 169 that had already been detected using other methods, and 20 brand new ones. The really interesting thing about these galaxy clusters is the huge range of masses they encompass — between one and fifteen hundred trillion times the mass of the Sun. Galaxy clusters are extremely sensitive to the underlying framework that describes our universe, and so can shed light on the evolution and structure of the universe.
By working together with another experiment at the ESA, the XMM Newton X-ray observatory, 11 of the newly discovered galaxy clusters have already been confirmed. XMM-Newton has been able to get a closer look at some and reveal that two of the new clusters are in fact superclusters. That is, they are clusters of galaxy clusters, rather than simply clusters of galaxies.
Not content with studying the largest structures in the universe, Planck has also taken a look at the coldest.
Thanks to Planck, we can now detect material at lower temperatures than ever before. And we can do it more accurately than ever before, too. Astronomers working on the Planck mission have just finished looking at the results of the first all-sky survey of compact cold dust clumps in the Milky Way, and cool dust in other galaxies. These clumps are some of the coldest objects in the universe, and are key to understanding some of the hottest — cold, dusty clumps, like the ones seen by Planck, are believed to be sites of star formation.
These clumps have temperatures of only 7 to 16 degrees above absolute zero. Most of the clumps Planck found were only a few light years away from Earth, but some were up to eight thousand light years away*.
Though Planck was only able to look in detail at this dust in our own galaxy, the results are vital to understanding the behaviour of similar dust in other galaxies. When we look at galaxies that are further away, we also see them as they were further back in time. As we learn more about star formation in our own galaxy from these cold clumps, we will begin to have a better understanding of star formation in galaxies that are further away — and further back in time.
However, Planck has limitations, and these mean that it cannot look into the heart of these cold objects. This is where the ESA’s Herschel space observatory comes in. It has a much higher resolution than Planck and has no problem seeing the detailed structure of the clumps. Between them, Herschel and Planck can form a complete picture of the clumps at both small and large scales. With their help, we can effectively reel in far away galaxies for a closer look and learn about star formation throughout the history of the universe.
Cold dust clumps and galaxy clusters are just two of the interesting discoveries Planck has made in the two full sky surveys it’s completed since it launched in May 2009. It will continue to survey the sky until at least the end of 2011, but full results, including that new detailed picture of the CMB minus the noise, will not be published before early 2013. That might seem like a long way away, but these first results should keep astronomers busy for a little while yet. Then they can get on with the job of studying the CMB, which will no doubt keep them busy for an even longer time to come.
*A light year is roughly three thousand billion miles. For comparison, the Sun is just less than a hundred billion miles, or eight light minutes, from Earth