Why mapping the galaxy will be child’s play

Within the Draco constellation, in the far northern sky, scientists have discovered a star, 700 light years from Earth, that has a distinctly unhealthy appetite. It is devouring its stellar companion. As the smaller of the two spins round the larger, the little cannibal is ripping streams of matter from its partner. Even odder, both stars have used up all their hydrogen fuel and now face a spectacular end to their existences – as fodder for supernovae explosions.For good measure, the two stars of Gaia14aae perfectly eclipse each other, as seen from Earth, a feature that could prove to be of key importance for astronomers. Eclipses allow scientists to calculate the masses of binary stars with unprecedented precision, and will give them a handle on understanding the behaviour of this extraordinary pair as they circle each other in their stellar dance of death.

But what also excites scientists is the fact that it took groups of professional astronomers working with amateur colleagues to pinpoint this extraordinary object – and that teamwork could prove to be a powerful force in future. Indeed, many believe that amateurs, including children, working with professionals, could prove a highly effective combination.

“In the near future we are going to be finding so many more interesting objects in our galaxy, and because telescope time is severely limited at the really big observatories, we won’t be able to make sense of those discoveries without a lot of help from amateurs and schoolchildren,” says Dr Heather Campbell of Cambridge University. “Astronomy is going to change.”

At the heart of this revolution is the European Space Agency star-mapper satellite Gaia, which was launched in December 2013. Over its five-year lifetime, Gaia is scheduled to study more than a billion stars, with each object being examined 70 times. On each of these 70 occasions, each individual star’s spectrum, brilliance and motion will be measured and carefully analysed. The process will transform our understanding of our galaxy – and deluge astronomers with data.

“We want to know where the stars are in our galaxy and how they are moving around,” adds Campbell, who is based at Cambridge’s Institute of Astronomy, which acts as a processing centre for data from Gaia. “From this information we can work out how our galaxy is evolving and how it formed in the first place. We also want to find peculiar, unusual stars that might tell us about unexpected forces that might be in play there. Gaia is the perfect device for doing that.”

Gaia completed its six-month commissioning period last year and is now getting down to its mapping work in earnest, making around 40 million observations a day. “We have already had a fair number of alerts from the satellite to tell us it has spotted something interesting. Until now, these alerts have been handled by astronomers who have passed these on to the astronomical community,” says Campbell.

“Very soon, that stream of discoveries of potentially interesting objects is going to turn into a flood, however. Alerts will then have to be processed and released automatically by computers. We will then need as much support as we can get to make the most of that data flood.” And that is why the binary star Gaia14aae is considered so important: its secrets were revealed by professional and amateur astronomers working as a team, a model for the future of astronomy.

Originally pinpointed last year by Gaia, which provided its name, the binary revealed itself in the satellite’s instruments after it became five times brighter over the course of a single day. “Gaia has two mirrors on board,” Campbell explains. “These look at the same patch of sky but with a 106-minute time difference between them. That means you can see objects that change in brightness really quickly – which is how we found our cannibal.”

Variable stars are relatively common. However, such dramatic, swift transitions in brightness as demonstrated by Gaai14aae are rare. This variation occurs because it is made up of two objects that orbit each other at an astonishing speed. “In fact, the two component stars complete their orbits faster than the minute hand of a clock,” says astronomer Professor Tom Marsh of Warwick University. As a result, the system produces a total eclipse every 50 minutes.

And eclipses turn out to be of considerable value. Binary stars are also quite common, but those that have orbits that are seen edgewise from Earth are relatively rare – and important. Seen from our planet, one star passes in front of the other as they go round each other. The result is an eclipse, a feature that allows astronomers to make very detailed measurements of the stars’ motions and then, from that information, to obtain very accurate estimates of their masses and sizes. This accuracy is not usually possible with non-eclipsing twin stars.

Enrique de Miguel Agustino, from Huelva in Spain, is one of the team of amateur observers who worked on the Gaia14aae project. He said: “An eclipsing binary system offers an invaluable opportunity to measure the properties of individual stars like mass and size – which are otherwise extremely difficult to measure.”

Finally, there is the make-up of the two stars. The smaller is of a type known as a white dwarf. It is immensely hot and also incredibly dense. A teaspoonful of its material would weigh as much as an elephant. The effect of this super-hot, super-dense star on its companion has been spectacular. The latter has swollen up and has been dragged closer and closer to the smaller star, which is now pulling vast streams of matter from its larger companion. Thus the little cannibal star is devouring its victim as it whirls around it.

For his part, Agustino recalls how he heard about the binary’s existence last year. “The Gaia alerts group issued a short note reporting spectroscopic measurements of several stars,” he says. One of these was named Gaia14aae. “I read the telegram on 20 October and that night aimed one my telescopes at it. It was no longer bright. Indeed it was very faint and very close to the limit of my telescope.”

Nevertheless, Agustino, who is a member of the group of amateur astronomers known as the Center for Backyard Astrophysics, which is run by Joe Patterson in New York, was convinced he had found an eclipsing cannibal star and reported his work to the Gaia Alert team. Subsequent observations by bigger telescopes proved he was correct. He had helped to uncover a doubly rare stellar object: a cannibal star whose eclipses are visible from Earth. In addition, he had found one that along with its partner star had burned up virtually all their hydrogen fuel and turned it to helium. (Ultimately, that helium will be burned up by the stars and they could eventually explode as supernovae.)

Only a few dozen such helium-rich cannibal binaries have ever been discovered and only one of these is an eclipsing binary. Gaia14aae thus provides astronomers with an very important new source of information, because the intense gravitational forces let loose within such pairs of stars make them prime candidates to be generators of one of the most important but as yet undetected forces in the universe: gravitational waves.

Predicted by Einstein but still unobserved despite intense efforts by physicists, gravitational waves are eddies in the fabric in space-time that are believed to be triggered by cataclysmic astronomical events, like those released by cannibal, helium-rich stars such as Gaia14aae.

And that is not all. At the ends of their lives, cannibal stars soak up more and more matter from their partners and erupt as supernovae. In particular, they explode as Type 1A supernovae, which also have special cosmological significance. Campbell explains: “Type 1A supernovae appear with almost the exact same brightness anywhere in the universe, which provides science with an exact measure of the distance of those supernovae and the galaxies in which they are embedded.”

Crucially, by studying the brightnesses of Type 1A supernovae, scientists were able to show in 1998 that very distant galaxies are moving away from each other at faster and faster speeds and concluded that a force, called dark energy, permeates the universe and is pushing objects apart, accelerating the expansion of the universe. “We use Type 1A supernovae to measure the universe but we still do not know exactly what processes trigger these events,” added Campbell. “Again, Gaia14aae could play a very important role in putting that right.”

Thanks to Gaia – and some hard-working amateur astronomers – key information about the cosmos is now at hand. “This is an exquisite system,” says Marsh. “It fairly whets the appetite for the many new discoveries we now expect from Gaia.”

As to the teams of astronomers that will be needed to take advantage of the flood of data that is now pouring from Gaia, one set of researchers will have an unexpected source. They will be British schoolchildren.

Fraser Lewis, of the Faulkes Telescope Project explains: “We were set up by the UK entrepreneur Dill Faulkes who built two 2-metre telescopes – one in Australia and one in Hawaii – which he dedicated for use by schoolchildren. They could use them to observe the night sky on other side of the world while it was still daylight over here. And the aim was straightforward: to stimulate interest in science and technology.

“Those two telescopes are now part of a larger network known as Las Cumbres Observatory Global Telescope Network, which has a further nine telescopes in different parts of the world. Schoolchildren can program them in real time, watch as their observations are being made and then use the results for work in the classroom.”

More than 25% of observing time on the network is used by British schoolchildren under the guidance of their teachers. “They have a free range of what they want to use in terms of co-ordinates, exposure time and other variables,” adds Lewis. “The results are theirs to use for their research as well.”

Lewis believes Gaia could transform the work of these fledgling scientists. “Professional astronomers are going to be overwhelmed when Gaia gets going and its data really starts pouring in. Schoolchildren using the telescope network could make a real difference – along with adult amateur astronomers using their own telescopes – in helping scientists direct their big observatories towards the most promising objects found by Gaia. This has enormous potential.”