The Cosmic Shredder and the Magnetar

Dec 15, 2005
An artist's impression of the Swift spacecraft with a gamma-ray burst going off in the background. Credit: Spectrum Astro.

No, it is not the title of the next Harry Potter book - but the latest discoveries from NASA's Swift mission which is studying gamma-ray bursts (GRB's) - the most powerful explosions occurring in the Universe. As reported in Nature today, scientists from the UK, USA, Italy and Sweden have witnessed the probable destruction of a neutron star by a black hole.

In a further Nature paper also issued today, astronomers from the University of Hertfordshire have discovered that some of the "short" gamma-ray bursts occur much closer to home than previously thought and could result from the tearing apart of an exotic object called a magnetar.

Every couple of days or so a burst of gamma rays will appear randomly from any direction in the sky. Most of these events last a few tens of seconds. These "long bursts" are thought due to the collapse of a massive star which forms a black hole. Occasionally, however, a much shorter duration event is seen (lasting less than 2 seconds). The origin of these "short bursts" is one of the great unsolved mysteries in astronomy.

Observations made by Swift and other telescopes, including the European Southern Observatory's Very Large Telescope, over the last six months indicate that some short bursts may be due to the merger of two neutron stars - dense cores of dead stars. These can combine after orbiting each other for perhaps hundreds of millions of years to form a black hole which powers a brief flash of gamma-rays. The light from such an event will decay away very quickly. The new observation suggests that another, rarer mechanism may be involved in the formation of some short bursts in which the objects that merge are a black hole and a neutron star.

Dr. Paul O'Brien from the University of Leicester says "This short burst emitted X-rays for over a day after the bright gamma-ray flash had faded. Multiple X-ray flares were also seen. This all suggests a binary system of a black hole and a dense neutron star was involved. The neutron star, around the mass of the Sun, was literally torn apart after coming too close to the black hole. At peak, the total power output was equivalent to about a million, billion Suns."

Professor Andrew King, also from the University of Leicester says "The black hole shredded the neutron star and either swallowed it in chunks or it formed a disc around the black hole which was then accreted. This could be the first ever observation of a black hole-neutron star binary system."

Data from previous missions is not forgotten though - astronomers from the University of Hertfordshire, have made a new and unexpected discovery. By statistically comparing the distribution of the nine years of short-duration bursts detected by the Compton Gamma Ray Observatory with the distribution of galaxies within about 300 million light years of the Milky Way, they conclude that around 15% originate from these relatively nearby galaxies. This is more than ten times closer than previously thought. A report of this work also appears in Nature this week.

These nearby short bursts, could, like their more distant brethren, result from catastrophic collisions of neutron stars, but if so then their outbursts must be much weaker. Alternatively, they could be a fundamentally different kind of explosion. A prime candidate would be an exotic object called a magnetar, a lone neutron star with a magnetic field 100,000 billion times that of the Earth, tearing itself apart due to enormous magnetic stresses.

An example of such an explosion was seen a year ago coming from a magnetar in our own galaxy, the Milky Way, so it seems reasonable to expect they should occur occasionally in other galaxies too, said Dr Nial Tanvir from the University of Hertfordshire. If so, they would look very much like short-duration gamma-ray bursts. He continues, "Although we still don't know for sure what produces the short duration gamma-ray bursts, this is a crucial breakthrough in astronomy as knowing where a phenomenon occurs is often the first step towards understanding it."

Since its launch on 20 November 2004, Swift has observed over 100 GRB's. Swift's power lies in its ability to detect a fast-fading burst and then turn autonomously to point sensitive telescopes at the burst before it has faded. Dr. Julian Osborne, Lead Investigator for Swift at the University of Leicester says "Swift is unique in being able to observe the fading X-ray light from a GRB so quickly after the gamma-ray flash. The accurately determined position in this case was sent to observers on the ground who found the host galaxy for the burst within a few hours. This particular burst occurred four billion light years from Earth."

Source: PPARC

Explore further: Meteorites yield clues to Martian early atmosphere

add to favorites email to friend print save as pdf

Related Stories

ISOLDE sheds light on dying stars

Apr 04, 2014

What happens inside a dying star? A recent experiment at CERN's REX accelerator offers clues that could help astrophysicists to recalculate the ages of some of the largest explosions in the universe.

Birth of black hole kills the radio star

Dec 20, 2013

Astronomers led by a Curtin University researcher have discovered a new population of exploding stars that "switch off" their radio transmissions before collapsing into a Black Hole.

Recommended for you

Meteorites yield clues to Martian early atmosphere

2 hours ago

(Phys.org) —Geologists who analyzed 40 meteorites that fell to Earth from Mars unlocked secrets of the Martian atmosphere hidden in the chemical signatures of these ancient rocks. Their study, published ...

Let's put a sailboat on Titan

5 hours ago

The large moons orbiting the gas giants in our solar system have been getting increasing attention in recent years. Titan, Saturn's largest moon, is the only natural satellite known to house a thick atmosphere. ...

Image: Rosetta's Philae lander snaps a selfie

5 hours ago

Philae is awake… and taking pictures! This image, acquired last night with the lander's CIVA (Comet nucleus Infrared and Visible Analyzer) instrument, shows the left and right solar panels of ESA's well-traveled ...

User comments : 0

More news stories

Meteorites yield clues to Martian early atmosphere

(Phys.org) —Geologists who analyzed 40 meteorites that fell to Earth from Mars unlocked secrets of the Martian atmosphere hidden in the chemical signatures of these ancient rocks. Their study, published ...

Let's put a sailboat on Titan

The large moons orbiting the gas giants in our solar system have been getting increasing attention in recent years. Titan, Saturn's largest moon, is the only natural satellite known to house a thick atmosphere. ...

ESO image: A study in scarlet

This new image from ESO's La Silla Observatory in Chile reveals a cloud of hydrogen called Gum 41. In the middle of this little-known nebula, brilliant hot young stars are giving off energetic radiation that ...

How kids' brain structures grow as memory develops

Our ability to store memories improves during childhood, associated with structural changes in the hippocampus and its connections with prefrontal and parietal cortices. New research from UC Davis is exploring ...

Gate for bacterial toxins found

Prof. Dr. Dr. Klaus Aktories and Dr. Panagiotis Papatheodorou from the Institute of Experimental and Clinical Pharmacology and Toxicology of the University of Freiburg have discovered the receptor responsible ...