China's enormous Five-Hundred-Meter Aperture Spherical Telescope (FAST) has hit the headlines this week after state media reported it had found mysterious signals from space.
There was speculation that the signals may represent evidence of alien life, though scientists involved have said it is more likely that the signals were just interference from Earth.
In any case, the world's largest filled-aperture radio telescope, with its 1,600 ft dish, has made a number of important discoveries before. Earlier this year astronomers announced that it had discovered a rare repeating radio signal coming from deep space, and they're not quite sure what it is yet.
The fast radio burst, or FRB, is called 20190520B and was detected with the FAST radio telescope in China as part of a survey in 2019. The FRB was first detected as part of a 24-second scan, and the signal was identified many more times in follow-up observations in 2020.
FRBs are intense bursts of radio signals that can last just milliseconds and emit more energy in this time than our sun does in a year. Their origins are the subject of ongoing research, though exotic and extremely energetic types of stars known as magnetars are leading candidates.
The source of the signal has been traced to a dwarf galaxy around 3 billion light-years away from Earth. Observations have also suggested that the source of the signal is small.
In some ways the signal is similar to another repeating FRB detected in 2016 called FRB 121102, the very first FRB whose position was determined. Both signals demonstrate repeating bursts and persistent radio emissions between these bursts that come from a compact region.
"Now we have two like this, and that brings up some important questions," said Casey Law, a radio astronomy scientist at Caltech, in a National Radio Astronomy Observatory (NRAO) press release.
The fact that some FRBs repeat themselves and others don't suggests that there may be two different mechanisms at play that produce these signals, or that the objects producing them act differently at different stages.
Part of the scientific interest surrounding FRBs is that they can be used as tools to study the space between them and the Earth, since scientists can study the effect that this intervening space has on the signal.
However, that has proven not to be the case with FRB 190520. Though its location is estimated to be in a galaxy 3 billion light years away, the burst's signal suggests it should be more like 8 to 9.5 billion light years.
"This means that there is a lot of material near the FRB that would confuse any attempt to use it to measure the gas between galaxies," said Kshitij Aggarwal, a graduate student at West Virginia University in the NRAO press release. "If that's the case with others, then we can't count on using FRBs as cosmic yardsticks," he added.
One theory is that the source of the FRB is a neutron star surrounded by gas left behind by a supernova explosion. Either way the signal isn't the first to puzzle scientists.
FRBs aside, FAST has also played its part in detecting hundreds of pulsars, which are fast-spinning neutron stars left behind by the demise of massive stars that explode in a supernova.
Neutron stars are extremely dense stars that can be merely city-sized despite having a mass higher than that of the sun. It's sometimes said that a teaspoon of neutron star material would weigh a billion tons.
By the year 2010 approximately 1,800 pulsars had been found through radio detection while a further 70 had been found via gamma radiation according to Space.com.
The FAST telescope, despite becoming fully operational as recently as January 2020, has detected 509 new pulsars, according to the Chinese Academy of Sciences in December last year.
The telescope is also used by the alien-hunting SETI Institute to look for evidence of alien life among the stars via tell-tale radio signatures. Whilst the telescope is yet to find definitive proof of aliens, it's certainly helping out in other areas of astronomy.
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