When distant stars explode, they emit flashes of energy called gamma-ray bursts that are bright enough for telescopes on Earth to detect them. Studying these pulses, which can also come from the merger of some exotic astronomical objects such as black holes and neutron stars, can help astronomers like me understand the history of the universe.
Space telescopes detect an average of one gamma-ray burst per day, adding to the thousands of bursts detected over the years, and a community of volunteers makes research on these bursts possible.
On November 20, 2004, NASA launched the Neil Gehrels Swift Observatory, also known as Swift. Swift is a multi-wavelength space telescope that scientists are using to learn more about these mysterious gamma-ray flashes coming from the universe.
Gamma-ray bursts usually last for a very short period of time, from a few seconds to a few minutes, and the majority of their emissions are in the form of gamma rays, the part of the light spectrum that our eyes cannot see. Gamma rays contain a lot of energy and can damage human tissues and DNA.
Fortunately, Earth’s atmosphere blocks most gamma rays from space, but this also means that the only way to observe gamma-ray bursts is to use a space telescope like the Swift. Swift observed more than 1,600 gamma-ray bursts during his 19 years of observations. The information it collects from these explosions helps astronomers on the ground measure distances to these objects.
looking back in time
Data from Swift and other observatories have taught astronomers that gamma-ray bursts are some of the most powerful explosions in the universe. They are so bright that space telescopes like Swift can detect them from across the universe.
In fact, gamma-ray bursts are some of the most distant astrophysical objects observed with telescopes.
Since light travels at a finite speed, astronomers are effectively looking back in time as they peer further into the universe.
The most distant gamma-ray burst ever observed occurred so far away that its light took 13 billion years to reach Earth. When telescopes took photographs of this gamma-ray burst, they observed the event as it existed 13 billion years ago.
Gamma-ray bursts allow astronomers to learn about the history of the universe, including how the birth rate and mass of stars change over time.
Types of gamma ray bursts
Astronomers now know that there are basically two types of gamma-ray bursts; long and short. They are classified according to how long their pulse lasts. Long gamma-ray bursts have pulses longer than two seconds, and at least some of these events are related to supernovae, that is, exploding stars.
When a massive star, or a star at least eight times more massive than our Sun, runs out of fuel, it will explode as a supernova and turn into a neutron star or black hole.
Both neutron stars and black holes are extremely compact. If you shrunk the entire Sun to about 12 miles in diameter, or the size of Manhattan, it would be as dense as a neutron star.
Some particularly massive stars can also shoot out jets of light when they explode. These jets are concentrated beams of light supported by structured magnetic fields and charged particles. When these jets are directed toward Earth, telescopes like Swift will detect a gamma-ray burst.
On the other hand, pulses of short gamma ray bursts are less than two seconds long. Astronomers suspect that most of these short bursts are caused by the merger of two neutron stars or a neutron star and a black hole.
When a neutron star gets too close to another neutron star or black hole, the two objects will orbit around each other and lose some of their energy through gravitational waves, moving ever closer.
These objects eventually coalesce and emit short jets. When short jets are directed toward Earth, space telescopes can detect them as short gamma-ray bursts.
Classification of gamma ray bursts
Classifying bangs as short or long is not always that simple. Over the past few years, astronomers have discovered some strange short gamma-ray bursts associated with supernovae rather than expected mergers. And they found some long gamma-ray bursts related to mergers rather than supernovae.
These confusing situations show that astronomers do not fully understand how gamma-ray bursts occur. They suggest that astronomers need to better understand gamma-ray pulse patterns to better connect the pulses to their origins.
However, it is difficult to systematically classify pulse pattern, which is different from pulse duration. Impact patterns can be extremely diverse and complex. So far, even machine learning algorithms haven’t been able to accurately recognize all the detailed pulse structures that astronomers are interested in.
community science
My colleagues and I enlisted the help of volunteers through NASA to identify pulse structures. Volunteers learn to identify impact structures, then look at the images on their own computers and classify them.
Our preliminary results show that these volunteers, also called citizen scientists, can quickly learn and recognize the complex structures of gamma-ray pulses. Analyzing this data will help astronomers better understand how these mysterious explosions occur.
Our team hopes to learn whether more gamma-ray bursts in the sample challenge the previous classification of short and long. We will use the data to more accurately investigate the history of the universe through gamma-ray burst observations.
This citizen science project, called Burst Chaser, has grown since our initial results and we are actively recruiting new volunteers in our quest to investigate the mysterious origins behind these bursts.
This article is republished from The Conversation, an independent, nonprofit news organization providing facts and analysis to help you understand our complex world.
Written by Amy Lien University of Tampa.
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Amy Lien receives funding from the NASA Citizen Science Seed Fund Program.