Hubble sees too much infrared energy from gamma ray burst

The uncertainty of science: During a short gamma ray burst (GRB) that was observed in a distant galaxy on May, astronomers were baffled when measurements from the Hubble Space Telescope detected ten times more near infrared energy that they predict from this type of GRB.

GRBs fall into two classes. First there are the long bursts, which are thought to form from the collapse of a massive star into a black hole, resulting in a powerful supernova and GRB. Second there are the short bursts, which scientists think occur when two neutron stars merge.

The problem with this GRB is that though it was short and somewhat similar to other short GRBs across most wavelengths, in the near infrared Hubble detected far too much energy.

“These observations do not fit traditional explanations for short gamma-ray bursts,” said study leader Wen-fai Fong of Northwestern University in Evanston, Illinois.

…Fong and her team have discussed several possibilities to explain the unusual brightness that Hubble saw. While most short gamma-ray bursts probably result in a black hole, the two neutron stars that merged in this case may have combined to form a magnetar, a supermassive neutron star with a very powerful magnetic field. “You basically have these magnetic field lines that are anchored to the star that are whipping around at about a thousand times a second, and this produces a magnetized wind,” explained Laskar. “These spinning field lines extract the rotational energy of the neutron star formed in the merger, and deposit that energy into the ejecta from the blast, causing the material to glow even brighter.”

What is intriguing about their theory is that this merger of two neutron stars simply resulted in a larger neutron star, not a black hole. This new neutron star was also a magnetar and pulsar, but unlike a black hole, it was a still-visible physical object. And yet its creation in this GRB produced more energy.

When GRBs were first discovered, I was always puzzled why so many astronomers seemed to insist there must be a single explanation for them. With time, when two classes of GRBs were discovered, this assumption was then replaced with the equally puzzling insistence that only two types of events explained them.

It seemed to me that that such explosions had too many potential variables, and could easily have a wide range of causes, though all related to the destruction or merger of massive stars. As the data continues to accumulate this now appears increasingly the case.

Astronomers detect neutron star merger in both light and gravitational waves

Big news! Astronomers from dozens of telescopes on the ground and in space have observed for the first time the light burst caused by the merger of two neutron stars because earlier observations of the merger’s gravitational wave and gamma ray burst told them where to look in the sky.

On 17 August 2017 the NSF’s Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States, working with the Virgo Interferometer in Italy, detected gravitational waves passing the Earth. This event, the fifth ever detected, was named GW170817. About two seconds later, two space observatories, NASA’s Fermi Gamma-ray Space Telescope and ESA’s INTErnational Gamma Ray Astrophysics Laboratory (INTEGRAL), detected a short gamma-ray burst from the same area of the sky.

The LIGO–Virgo observatory network positioned the source within a large region of the southern sky, the size of several hundred full Moons and containing millions of stars. As night fell in Chile many telescopes peered at this patch of sky, searching for new sources. These included ESO’s Visible and Infrared Survey Telescope for Astronomy (VISTA) and VLT Survey Telescope (VST) at the Paranal Observatory, the Italian Rapid Eye Mount (REM) telescope at ESO’s La Silla Observatory, the LCO 0.4-meter telescope at Las Cumbres Observatory, and the American DECam at Cerro Tololo Inter-American Observatory. The Swope 1-metre telescope was the first to announce a new point of light. It appeared very close to NGC 4993, a lenticular galaxy in the constellation of Hydra, and VISTA observations pinpointed this source at infrared wavelengths almost at the same time. As night marched west across the globe, the Hawaiian island telescopes Pan-STARRS and Subaru also picked it up and watched it evolve rapidly.

Press releases today from numerous other observatories are too numerous to link here, and most essentially say the same thing. The key facts so far gleaned however are intriguing:

Distance estimates from both the gravitational wave data and other observations agree that GW170817 was at the same distance as NGC 4993, about 130 million light-years from Earth. This makes the source both the closest gravitational wave event detected so far and also one of the closest gamma-ray burst sources ever seen

This event also highlights the advantages of observing the universe in as many ways as possible. Some phenomenon get to us sooner, and thus provide us clues on where to look with other tools. Without the gravitational wave and gamma ray burst detectors, on Earth and in space, the other optical and infrared telescopes would have almost certainly not have recorded this merger.

A developing new astronomical mystery

Radio astronomers in Australia have recently detected a number of new mysterious radio bursts, dubbed fast radio bursts because of their nature, coming from outside our galaxy whose cause presently has no clear explanation.

An unprecedented double burst recently showed up along with four more of these flashes, researchers report online November 25 at arXiv.org.

Fast radio bursts, first detected in 2007, are bright blasts of radio energy that last for just a few milliseconds and are never seen again. Until now, astronomers had cataloged nine bursts that appeared to originate well outside the Milky Way. Yet, follow-up searches with nonradio telescopes for anything that might be pulsing or exploding keep coming up empty.

This mystery is similar to that of gamma ray bursts (GRBs), which were first discovered in the 1960s. About once a day there would be a short burst of gamma ray energy coming from scattered random directions in the sky, but no other radiation in any other wavelength. For decades astronomers didn’t know if the GRBs were coming from just outside our atmosphere or from billions of light years away. Finally, in the 1990s they pinned their location to the deaths of stars in distant other galaxies. As noted by one scientist at a conference, “GRBs signal the daily formation of a new black hole.”

Fast radio bursts are more intriguing. Because of their wavelengths and random locations on the sky, astronomers seem confident that they are occurring outside the Milky Way. However, in the eight years since their discovery only a handful have been detected, making it extremely difficult to study them. Nonetheless, they are significant because they signal some cataclysmic event far away, likely the death of a star in a way not yet understood or predicted. Finding out what that event is will produce important information about the evolution of our universe.

It just might take decades for this new mystery to be solved. Stay tuned!

New data from a neutrino telescope in Antarctica had found that cosmic rays don’t come from gamma ray bursts, as had been believed by astronomers.

The uncertainty of science: New data from a neutrino telescope in Antarctica has found that cosmic rays don’t come from gamma ray bursts, as had been believed by astronomers. You can read the paper here. [pdf]

Which means that astronomers at this moment have no idea what produces these high energy cosmic rays.