Immense set of mysterious fast radio bursts

An international team of astronomers recently observed more than 1,650 fast radio bursts (FRBs) detected from one source in deep space, which amounts to the largest set -- by far -- of the mysterious phenomena ever recorded.

More than a decade after the discovery of FRBs, astronomers are still baffled by the origins of the millisecond-long, cosmic explosions that each produce the energy equivalent to the sun's annual output.

In a study published in the Oct. 13 issue of the journal Nature, scientists -- including UNLV astrophysicist Bing Zhang -- report on the discovery of a total of 1,652 independent FRBs from one source over the course of 47 days in 2019. The source, dubbed FRB 121102, was observed using the Five-hundred-meter Aperture Spherical Telescope (FAST) in China, and represents more FRBs in one event than all previous reported occurrences combined.

"This was the first time that one FRB source was studied in such great detail," said Zhang, one of the study's corresponding authors. "The large burst set helped our team home in like never before on the characteristic energy and energy distribution of FRBs, which sheds new light on the engine that powers these mysterious phenomena."

Since FRBs were first discovered in 2007, astronomers worldwide have turned to powerful radio telescopes like FAST to trace the bursts and to look for clues on where they come from and how they're produced. The source that powers most FRBs is widely believed to be magnetars, incredibly dense, city-sized neutron stars that possess the strongest magnetic fields in the universe. And while scientists are gaining greater clarity on what produces FRBs, the exact location of where they occur is still a mystery.

A mystery that recent results may be starting to unravel.

According to Zhang, there are two active models for where FRBs come from. One could be that they come from magnetospheres, or within a magnetar's strong magnetic field. Another theory is that FRBs form from relativistic shocks outside the magnetosphere traveling the speed of light.

"These results pose great challenges to the latter model," says Zhang. "The bursts are too frequent and -- given that this episode alone amounts to 3.8% of the energy available from a magnetar -- it adds up to too much energy for the second model to work."

The bursts were measured by FAST within a total of 59.5 hours over 47 days from Aug. 29 to Oct. 29, 2019.

"During its most active phase, FRB 121102 included 122 bursts measured within a one-hour period, the highest repeat rate ever observed for any FRB," said Pei Wang, one of the article's lead authors from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC).

Researchers expect that FAST will continue to systematically investigate a large number of repeating FRBs in the future.

"As the world's largest antenna, FAST's sensitivity proves to be conducive to revealing intricacies of cosmic transients, including FRBs," said Di Li, the study's lead researcher from NAOC.

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Astronomers solve 900-year-old cosmic mystery surrounding Chinese supernova of 1181AD

A 900-year-old cosmic mystery surrounding the origins of a famous supernova first spotted over China in 1181AD has finally been solved, according to an international team of astronomers.

New research published today (September 15, 2021) says that a faint, fast expanding cloud (or nebula), called Pa30, surrounding one of the hottest stars in the Milky Way, known as Parker's Star, fits the profile, location and age of the historic supernova.

There have only been five bright supernovae in the Milky Way in the last millennium (starting in 1006). Of these, the Chinese supernova, which is also known as the 'Chinese Guest Star' of 1181AD has remained a mystery. It was originally seen and documented by Chinese and Japanese astronomers in the 12th century who said it was as bright as the planet Saturn and remained visible for six months. They also recorded an approximate location in the sky of the sighting, but no confirmed remnant of the explosion has even been identified by modern astronomers. The other four supernovae are all now well known to modern day science and include the famous Crab nebula.

The source of this 12th century explosion remained a mystery until this latest discovery made by a team of international astronomers from Hong Kong, the UK, Spain, Hungary and France, including Professor Albert Zijlstra from The University of Manchester. In the new paper, the astronomers found that the Pa 30 nebula is expanding at an extreme velocity of more than 1,100 km per second (at this speed, traveling from the Earth to the Moon would take only 5 minutes). They use this velocity to derive an age at around 1,000 years, which would coincide with the events of 1181AD.

Prof Zijlstra (Professor in Astrophysics at the University of Manchester) explains: "The historical reports place the guest star between two Chinese constellations, Chuanshe and Huagai. Parker's Star fits the position well. That means both the age and location fit with the events of 1181."

Pa 30 and Parker's Star have previously been proposed as the result of a merger of two White Dwarfs. Such events are thought to lead to a rare and relatively faint type of supernova, called a 'Type Iax supernova'.

Prof Zijlstra added: "Only around 10% of supernovae are of this type and they are not well understood. The fact that SN1181 was faint but faded very slowly fits this type. It is the only such event where we can study both the remnant nebula and the merged star, and also have a description of the explosion itself."

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