Starbursts offer a cosmic lab for physics

7 Mar 2013

Prof Lorraine Hanlon with 1:4 scale model of XMM-Newton, an ESA Earth-orbiting satellite observatory, donated to University College Dublin. The model is on permanent public display in the UCD Science Centre. Photo via University College Dublin

When Prof Lorraine Hanlon is not tracking down massive bursts of energy from exploding stars in the universe, she is working to get the public more engaged with physics. Claire O’Connell caught up with the University College Dublin (UCD) astrophysicist to find out more.

It’s easy to think of outer space as a serene place, but it can get pretty violent at times. When a star explodes, it releases enormous amounts of energy. And when a huge star explodes it can provide a kind of cosmic lab for studying physics that would be impossible to recreate on Earth.

That’s according to Prof Lorraine Hanlon, associate professor at UCD’s School of Physics, who has been tracking down the ‘gamma-ray bursts’ released by massive exploding stars.

From plane spotting to star spotting

Hanlon became interested in astrophysics not only through her love of physics in school, but also her keen interest in flight, she recalls. Growing up in Dublin, she and a friend would cycle to the airport to watch the aircraft come and go. “We would have our radios so we could listen to the control towers,” she says.

Today, Hanlon trains her sights a little further, watching for signs that stars have collapsed and issued bursts of radiation.

“In some cases the end-of-life star burns out as a supernova, releasing energy mainly in the form of visible light,” she explains – but she and her colleagues look for even bigger events.

“When a very large star collapses – maybe one that is 50 or more times the mass of our own sun – instead of producing its energy in visible light over many months it produces most of its energy in gamma-ray wavelengths in a matter of tens of seconds,” says Hanlon. “It fires all that radiation out initially in a huge burst, and then there is a remnant, an ember or glow that we can see over a longer time, as well.”

Patrolling the skies

Such monumental bursts kick off about once a day in our skies, says Hanlon, who uses data from a European Space Agency satellite called INTEGRAL to help pick them out and analyse them.

INTEGRAL has plenty else going on – its instruments search for black holes in our galaxy and have also allowed scientists to examine how chemical elements get spread around the galaxy when stars explode – but it also picks up bursts of gamma-ray radiation as it patrols the skies.

When it spots a burst, INTEGRAL tells robotic telescopes on Earth when and where it is happening, so that ground-based observatories can map the visible light or ‘ember‘ of the burst and build up an even better picture of the event, explains Hanlon.

Using INTEGRAL data, then-PhD student Suzanne Foley uncovered not only massive explosions but faint gamma-ray bursts, too. To borrow that moment when Father Ted explains to Dougal that the cows look small because they are far away, could it be that those gamma-ray bursts are faint because they come from stars that are more distant?   

“We looked at that and it seems not,” Hanlon says, and laughs. “It seems that these faint bursts are correlated with relatively local structures in the universe. That has been confirmed independently, but we need more data to understand these events better.”

Future observations

INTEGRAL’s mission is due to finish at the end of 2014, so to pave the way for future observations, Hanlon is actively involved in developing new and more sensitive technology to detect gamma-ray bursts.  

“It’s a challenging wavelength to work on and we are collaborating with scientists in Europe and with Irish companies to develop new ways of looking at gamma rays,” she explains, adding that the energetic bursts offer a kind of cosmic lab.

“They give us access to conditions that we can’t recreate on the ground. The Large Hadron Collider in Geneva can produce particles with energies that help us understand the physics of the early universe, but building a machine on Earth that could replicate the conditions in gamma-ray bursts is not on the horizon. These collapsing stars are laboratories to help us understand physical processes that we couldn’t possibly imagine setting up here.”

Public physics

As well as detecting and dissecting cosmic explosions, Hanlon is interested in engaging more people with the wonders of physics and astronomy. She is involved in GLORIA, an EU-funded initiative to link robotic telescopes around the world so that the public can make their own observations.

“It means that people can get their own information from telescopes instead of analysing the data that other people have taken over the years, and then they can do their own projects with that information,” explains Hanlon.

Already the GLORIA team has brought events, such as the transit of Venus last year and the recent near-Earth asteroid, to a wider audience with the telescopes. There’s a YouTube channel, too, with short clips that highlight the “weird stuff” that goes on in the universe, explains Hanlon.

She has also developed a close collaboration with artist Emer O Boyle, who has been engaging with the physics community in UCD. They now run a ‘Tunnelling Art and Physics’ module for undergraduates in UCD and the National College of Art and Design, where students explore concepts in physics and how they could be represented.

O Boyle has been working with the research staff, too, and the resulting artwork has been inspired by those conversations, explains Hanlon. “I think it’s a brilliant initiative,” she says. “The scientists very often don’t realise how amazing what they are doing is, but by reflecting it off the artists and getting excited about it, the resulting art can engage more people.”

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Dr Claire O’Connell is a scientist-turned-writer with a PhD in cell biology and a master’s in science communication