I regularly help out with Astronomy in the City here at the University. Our most recent event was a Christmas special, and we gave a talk on 12 festive highlights covering events past, present and future, somewhat biased towards our research interests. Here is our count-down again.
A Newton under an apple tree
Isaac Newton, arguably the greatest physicist of all time, was born on 25 December 1642. I expect he may have got many joint birthday–Christmas presents. Newton is most famous for his theory of gravity, which he allegedly thought up after being hit on the head by a falling apple. Realising that the same force could be responsible for mundane things like falling as for keeping celestial bodies such as the planets in their orbits, was a big leap (or fall?). Netwon’s theory of gravity is highly successful, it’s accurate enough to get us to the Moon (more on that later) and only breaks down for particularly strong gravitational fields. That’s when you need Einstein’s theory of general relativity.
Newton may have been a Pink Floyd fan, we may never know.
Newton also did much work on optics. He nearly blinded himself while prodding his eye to see how that would affect his sight. Even smart people do stupid things. Newton designed the first practical reflecting telescope. Modern astronomical telescopes are reflecting (using a mirror to focus light) rather than refracting (using a lens). The first telescope installed at the University’s Observatory was a Newtonian reflector.
Newton’s reflecting telescope, one of the treasures of the Royal Society. Newton was President of the Royal Society, as well as Master of the Royal Mint, Member of Parliament for University of Cambridge and Lucasian Professor of Mathematics. It’s surprising he had any time for alchemy.
2 clear nights
At Astronomy in the City, we have talks on the night sky and topics in astrophysics, a question and answer session, plus some fun activities after to accompany tea and biscuits. There’s also the chance to visit the Observatory and (if it’s clear) use the Astronomical Society’s telescopes. Since the British weather is so cooperative, we only had two clear observing nights from this year’s events (prior to the December one, which was clear).
If you had made one of the clear nights, you could have viewed the nebulae M78 and M42, or Neptune and its moons. Neptune, being one of the ice giants, is a good wintry subject for a Christmas talk. It’s pretty chilly, with the top of its atmosphere being −218 °C. You don’t have a white Christmas on Neptune though. It’s blue colouring is due to methane, which with ammonia (and good old water) makes up what astronomers call ices (I guess you should be suspicious of cocktails made by astronomers).
One of the most exciting views of the year was supernova 2014J, back in January. This was first spotted by students at University College London (it was cloudy here at the time). It’s located in nearby galaxy M82, and we got some pretty good views of it. You can see it out-shine its entire host galaxy. Supernovae are pretty bright!
3 components of a cluster
Galaxy clusters are big. They are the largest gravitationally-bound objects in the Universe. They are one of astrophysical objects that we’re particularly interested in here at Birmingham, so they’ll pop up a few times in this post.
Galaxy clusters have three main components. Like trifles. Obviously there are the galaxies, which we can see because they are composed of stars. Around the galaxies there is lots of hot gas. This is tens of millions of degrees and we can spot it because it emits X-rays. Don’t put this in your trifles at home. The final component is dark matter, the mysterious custard of our trifle. We cannot directly see the dark matter (that’s why it’s dark), but we know its there because of the effects of its gravity. We can map out its location using gravitational lensing: the bending of light by gravity, one of the predictions of general relativity.
Different views of cluster Abell 209. The bottom right is a familiar optical image. Above that is a smoothed map of infra-red luminosity (from old stars). The top left is a map of the total mass (mostly due to dark matter) as measured with gravitational lensing. The bottom left is a X-ray map of the hot intergalactic gas. Credit: Subaru/UKIRT/Chandra/University of Birmingham/Nordic Optical Telescope/University of Hawaii.
Measuring the dark matter is tricky, but some of the work done in Birmingham this year shows that is closely follows the infra-red emission. You can use the distribution of jelly in your trifle to estimate how much custard there should be. In the picture above of galaxy cluster Abell 209, you can see how similar the top two images are. Using the infra-red could be a handy way of estimating the amount of dark matter when you don’t have access to gravitational-lensing measurements.
4 km long laser arms
A highlight for next year: the first observing run of Advanced LIGO. Advanced LIGO is trying to make the first direct detection of gravitational waves. Gravitational waves are tiny stretches and squeezes in spacetime, to detect them you need to very carefully measure the distance between two points. This is where the 4 km arms come in: the Advanced LIGO detectors bounce lasers up and down their arms to measure the distance between the mirrors at the ends. The arms need to be as long as possible to make measuring the change in length as easy as possible. A typical change in length may be one part in 1021 (that is 1,000,000,000,000,000,000,000 or one sextillion… ). For comparison, that’s the same as measuring the distance between the Earth and the Sun to the diameter of a hydrogen atom or the distance from here to Alpha Centuri to the width of a human hair.
Aerial shot of LIGO Livingston, Louisiana. Two arms come out from the central building, one goes up the middle of the picture, the other goes off to the left out of shot. I think this gives a fair indication of the scale of the detectors. In addition to the instruments in Livingston, there is another LIGO in Hanford, Washington.
Making such an precise instrument is tricky. At least twice as tricky as remembering the names of all seven of the dwarfs. We shouldn’t be Bashful about saying how difficult it is. We need to keep the mirrors extremely still, any little wibbles from earth tremors, nearby traffic, or passing clouds need to be filtered out. Lots of clever Docs have been working on cunning means of keeping the mirrors still and then precisely measuring their position with the lasers. Some of that work was done here in Birmingham, in particular some of the mirror suspension systems. We’ll be rather Grumpy if those don’t work. However, things seem to be going rather well. Getting the mirrors working isn’t as simple as pushing a big red button, so it takes a while. On the 3 December, which is when we gave this talk at Astronomy in the City, the second detector achieved its first full lock: lock is when the mirrors are correctly held stably in position. This made me Happy. Also rather Sleepy, as it was a late night.
Team inspecting the optical systems at LIGO Livingston back at the start of 2014. (It’s a bit harder to detect the systems now, since they’re in a vacuum). You need to wear masks in case you are Sneezy, you’d feel rather Dopey if you ruined the mirrors by sneezing all over them. Credit: Michael Fyffe
5 (or more) planet-forming rings!
ALMA image of the young star HL Tau and its protoplanetary disc. The gaps in the disc indicate the formation of planets that sweep their orbits clear of dust and gas. Credit: ALMA, C. Brogan & B. Saxton
One of the most exciting discoveries of 2014 is this remarkable image of a planet-forming disc.There may be more than five planets, but it seemed like a shame not to fit this into our countdown here. The image is of the star HL Tauri. This is a young star, only a million years old (our Sun is about 4.6 billion years old). Remarkably, even at this young age, there seems to be indication of the formation of planets. The gaps are where planets have sucked up the dust, gas and loose change of the disc. This is the first time we’ve seen planet-formation in such detail, and matches predictions extremely well.
6 Frontier Fields
The six Frontier Fields are a group of six galaxy clusters that are being studied in unprecedented detail. They are being observing with three of NASA’s great observatories, the Hubble Space Telescope, the Spitzer Space Telescope (which observes in the infra-red) and the Chandra X-ray Observatory. These should allow us to measure all three components of the clusters (even the custard of the trifle). The clusters are all selected because the show strong gravitational lensing. This should give us excellent measurements of the mass of the clusters, and hence the distribution of dark matter.
Gravitational lensing by a galaxy cluster. The mass of the galaxy cluster bends spacetime. Light travelling through this curved spacetime is bent, just like passing through a lens. The amount of bending depends upon the mass, so we can weigh galaxy clusters by measuring the lensing. Credit: NASA, ESA & L. Calcada.
7 months until New Horizons reaches Pluto
New Horizons is a planetary mission to Pluto (and beyond). Launched in January 2006, New Horizons has been travelling through the Solar System ever since. In 2007 it made a fly-by of Jupiter, taking some amazing pictures. It is now just 7 months from reaching Pluto. This will give us the first ever detailed look at Pluto and its moons. You’ll need to wrap up warm if you wanted to head there yourself. I hope that New Horizons packed some mittens. New Horizons will tell us about Pluto and other icy (yes, that’s astronomers’ definition of ice again) items in the Kuiper belt.
Full trajectory of New Horizons, it’s come a long way! Credit: John Hopkins
New Horizons has been in hibernation for much of its flight. Who doesn’t like a good nap? New Horizons was woken up ahead of arriving at Pluto on 7 December. It got a special wake-up call from Russell Watson. I don’t think it has access to coffee though.
800 TB of data
This year’s Interstellar featured the most detailed simulations of the appearance of black holes. This involved a truly astounding amount of data. I’ve previously written about some of the science in Interstellar. I think it’s done a good at getting people interested in the topic of gravity. It’s scientific accuracy can be traced to the involvement of Kip Thorne, who has written a book on the film’s science (which might be a good Christmas present). Kip has done many things during his career, including being one of the pioneers of LIGO. After an exciting 2014 with the release of Interstellar, I’m sure he’s looking forward to 2015 and the first observations of Advanced LIGO too.
Light-bending around the black hole Gargantua in Interstellar. This shows the accretion disc about the black hole, the disc seen above and below the hole are actually the top and bottom of the disc behind the black hole. This extreme light-bending is a consequence of the extremely curved spacetime close to the black hole. This light-bending is exactly the same as the gravitational-lensing done by galaxy clusters, except much stronger!
999 Kepler exoplanets
When we gave the talk on 3 December, Kepler had discovered 998 exoplanets. It’s now 999, which I think means we get all the bonus points! Kepler is still doing good science, despite some technical difficulties. Kepler has been hugely successful. We now know that planets (as well as forming in quite short times) are common, that they are pretty much everywhere. Possibly even down the back of the sofa. Some of the work done here in Birmingham has been to estimate just how common planets are. On average, stars similar to the Sun have around 4 planets with periods shorter than 3 years (and radii bigger than 20% of Earth’s). That’s quite a few planets! But, if Christopher Nolan wants to direct another reasonably accurate sci-fi, we need to know how many of those are Earth-like. We don’t have enough data to work out details of atmospheres, but just looking at how many planets have a radius and period about the same as Earth’s, it seems that about 4% of these stars have Earth-like planets.
Kepler-186, the first system discovered with an Earth-sized planet on the edge of the habitable zone (where liquid water could exist), was discovered in 2014.
10 lunar orbits
A Christmas highlight from 1968. On December 21, Apollo 8 launched. This was the first manned mission to ever leave Earth orbit. On Christmas Eve, it entered into orbit about the Moon. It’s three-man crew of Frank Borman, James Lovell and William Anders were the first people ever to orbit a body other than the Earth. To date, only 24 men have ever done so. Of course, even fewer have actually walked on the Moon, perhaps we should go back? Jim Lovell was also on the ill-fated Apollo 13 mission (you may have seen the film), making him the only person to orbit the Moon on two separate occasions and never land. Apollo 8 was successful, it orbited the Moon 10 times, giving us the first ever peek at the dark side of the moon (not the Pink Floyd album). This was also the first viewing of an Earthrise. Their Christmas Eve broadcast was most watched TV broadcast at the time. After orbiting, Apollo 8 returned home, splashing down December 27. I’m guessing they had a good New Year’s celebration!
Earthrise taken by the crew of Apollo 8, Christmas Eve 1968. Credit: NASA
11 (10 ¾) years for Rosetta
This year we landed on a comet. Rosetta has received fair amount of press. It is an amazing feat, Rosetta was in space for almost 11 years before making its comet rendezvous. It’ll be doing lots of science form orbit, such as determining that comets are unlikely to have delivered water to Earth. Most of the excitement surrounded the landing of Philae on the surface of the comet. That didn’t go quite as planned, but still taught us quite a bit. Rosetta has been heralded as one of the science breakthroughs of 2014. We’ll have to see what 2015 brings.
Colour image (yes, it’s grey) of 67P/Churyumov-Gerasimenko from Rosetta. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
12 (or more) galaxies in a cluster
To finish up, back to galaxy clusters. Galaxy clusters grow by merging. We throw two trifles together to get a bigger one. As you might imagine, if you throw two triffles together, you don’t get a nice, neat trifle. The layers do tend to mix. For galaxy clusters, you can get layers separating out: dark matter passes freely through everything, so it isn’t affected by a collision. The gas, however, does feel the shock and ends up a turbulent mess. It has been suggested that turbulence caused by mergers could trigger star formation: you squeeze the gas and some of it collapses down into stars. However, recent observational work at Birmingham can’t find any evidence for this. We’ll have to see if this riddle gets unravelled in 2015.
The merging bullet cluster. A composite of an optical image (showing galaxies), an X-ray image (in red, showing the hot gas), and a map of the total mass (in blue, from gravitational lensing). Dark matter, making up most of the mass, has past straight through the collision without interacting. Credit: NASA/CXC/CfA/STScI/ESO/U.Arizona/M. Markevitch/D. Clowe