Invading black holes cause ‘cosmic flashes’

September 19, 2009 By Leave a Comment

Washington, September 19 (ANI): Mathematicians at the University of Leeds, UK, have determined that cosmic flashes, known as gamma ray bursts, are produced by jets of plasma that originate from invading black holes.

Gamma ray bursts are beams of high-energy radiation that are similar to the radiation emitted by explosions of nuclear weapons.

The orthodox model for this cosmic jet engine involves plasma being heated by neutrinos in a disk of matter that forms around a black hole, which is created when a star collapses.

But, mathematicians at the University of Leeds, have come up with a different explanation: the jets come directly from black holes, which can dive into nearby massive stars and devour them.

Their theory is based on recent observations by the Swift satellite, which indicates that the central jet engine operates for up to 10,000 seconds – much longer than the neutrino model can explain.

Mathematicians believe that this is evidence for an electromagnetic origin of the jets, that is, that the jets come directly from a rotating black hole, and that it is the magnetic stresses caused by the rotation that focus and accelerate the jet’s flow.

For the mechanism to operate, the collapsing star has to be rotating extremely rapidly.

This increases the duration of the star’s collapse as the gravity is opposed by strong centrifugal forces.

One particularly peculiar way of creating the right conditions involves not a collapsing star, but a star invaded by its black hole companion in a binary system.

The black hole acts like a parasite, diving into the normal star, spinning it with gravitational forces on its way to the star’s centre, and finally eating it from the inside.

“The neutrino model cannot explain very long gamma ray bursts and the Swift observations, as the rate at which the black hole swallows the star becomes rather low quite quickly, rendering the neutrino mechanism inefficient, but the magnetic mechanism can,” said Professor Komissarov from the School of Mathematics at the University of Leeds.

“Our knowledge of the amount of the matter that collects around the black hole and the rotation speed of the star allow us to calculate how long these long flashes will be – and the results correlate very well with observations from satellites,” he added. (ANI)

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Astronomers spot a pair of solar systems in the making

July 2, 2009 By Leave a Comment

Washington, July 2 (ANI): Two University of Hawaii astronomers have found a binary star-disk system in which each star is surrounded by the kind of dust disk that is frequently the precursor of a planetary system, which makes them solar systems in the making.

The astronomers in question are doctoral student Rita Mann and Dr. Jonathan Williams, who used the Submillimeter Array on Mauna Kea, Hawaii, to make the observations.

A binary star system consists of two stars bound together by gravity that orbit a common center of gravity.

Most stars form as binaries, and if both stars are hospitable to planet formation, it increases the likelihood that scientists will discover Earth-like planets.

This binary system, 253-1536, stands out as the first known example of two optically visible stars, each surrounded by a disk with enough mass to form a planetary system like our own.

It lies 1,300 light-years from Earth, in the famous Orion Nebula, the kind of rich cluster of stars that is a common birth environment for most stars in our Milky Way galaxy, including our Sun.

One of the disks was discovered in an image taken with the Hubble Space Telescope, but the other disk was hidden in the glare of the star.

Hubble saw only the disk shadow, so the amount of material and its capability for planet formation was unknown until the UH team made the SMA observations.

The two stars are 400 times farther from each other than Earth is from the Sun.

They would take 4,500 years, or about the length of human recorded history, to complete one orbit around their common center.

Both stars are only about a third the mass of our Sun and are much cooler and redder in color.

The larger disk in 253-1536 is also the most massive found in the Orion Nebula so far.

The discovery of this massive disk and the binary disk system improve our understanding of how common planet formation is in our Galaxy and place our Solar System in context. (ANI)

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Scientists find oldest isolated pulsar ever

February 27, 2009 By Leave a Comment

Washington, Feb 27 (ANI): With the help of NASA’s Chandra X-ray Observatory, scientists have found the oldest isolated pulsar ever detected in X-rays.

The pulsar, PSR J0108-1431 (J0108 for short), which is about 200 million years old, turns out to be surprisingly active.

Among isolated pulsars, ones that have not been spun-up in a binary system, it is over 10 times older than the previous record holder with an X-ray detection.

At a distance of 770 light years, it is one of the nearest pulsars known.

Pulsars are born when stars that are much more massive than the Sun collapse in supernova explosions, leaving behind a small, incredibly weighty core, known as a neutron star.

At birth, these neutron stars, which contain the densest material known in the Universe, are spinning rapidly, up to a hundred revolutions per second.

As the rotating beams of their radiation are seen as pulses by distant observers, similar to a lighthouse beam, astronomers call them “pulsars”.

Astronomers observe a gradual slowing of the rotation of the pulsars as they radiate energy away.

Radio observations of J0108 show it to be one of the oldest and faintest pulsars known, spinning only slightly faster than one revolution per second.

The surprise came when a team of astronomers led by George Pavlov of Penn State University observed J0108 in X-rays with Chandra.

They found that it glows much brighter in X-rays than was expected for a pulsar of such advanced years.

Some of the energy that J0108 is losing as it spins more slowly is converted into X-ray radiation. The efficiency of this process for J0108 is found to be higher than for any other known pulsar.

“This pulsar is pumping out high-energy radiation much more efficiently than its younger cousins,” said Pavlov. “So, although it’s clearly fading as it ages, it is still more than holding its own with the younger generations,” he added.

At its advanced age, J0108 is close to the so-called “pulsar death line,” where its pulsed radiation is expected to switch off and it will become much harder, if not impossible, to observe.

“We can now explore the properties of this pulsar in a regime where no other pulsar has been detected outside the radio range,” said co-author Oleg Kargaltsev of the University of Florida.

“To understand the properties of ‘dying pulsars,’ it is important to study their radiation in X-rays. Our finding that a very old pulsar can be such an efficient X-ray emitter gives us hope to discover new nearby pulsars of this class via their X-ray emission,” he added. (ANI)

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Stars become overweight due to ‘stellar cannibalism’

January 15, 2009 By Leave a Comment

London, Jan 15 (ANI): In a new research, scientists have discovered that the mysterious overweight stars known as blue stragglers are the result of ‘stellar cannibalism’ where plasma is gradually pulled from one star to another to form a massive, unusually hot star that appears younger than it is.

The research was part funded by the UK’s Science and Technology Facilities Council (STFC) and carried out by scientists at Southampton University and the McMaster University in Canada.

Blue stragglers are found throughout the Universe in globular clusters – collections of about 100, 000 stars, tightly bound by gravity.

According to conventional theories, the massive blue stragglers found in these clusters should have died long ago because all stars in a cluster are born at the same time and should therefore be at a similar phase.

These massive rogue stars, however, appear to be much younger than the other stars and are found in virtually every observed cluster.

“The origin of blue stragglers has been a long-standing mystery. The only thing that was clear is that at least two stars must be involved in the creation of every single blue straggler, because isolated stars this massive simply should not exist in these clusters,” said Dr Christian Knigge from Southampton University, who led the study.

“We’ve known of these stellar anomalies for 55 years now. Over time, two main theories have emerged: that blue stragglers were created through collisions with other stars; or that one star in a binary system was ‘reborn’ by pulling matter off its companion,” said Professor Alison Sills from the McMaster University.

The researchers looked at blue stragglers in 56 globular clusters.

They found that the total number of blue stragglers in a given cluster did not correlate with predicted collision rate – dispelling the theory that blue stragglers are created through collisions with other stars.

They did, however, discover a connection between the total mass contained in the core of the globular cluster and the number of blue stragglers observed within in.

Since more massive cores also contain more binary stars, they were able to infer a relationship between blue stragglers and binaries in globular clusters.

They also showed that this conclusion is supported by preliminary observations that directly measured the abundance of binary stars in cluster cores.

All of this points to “stellar cannibalism” as the primary mechanism for blue straggler formation.

According to Dr Knigge, “This is the strongest and most direct evidence to date that most blue stragglers, even those found in the cluster cores, are the offspring of two binary stars.” (ANI)

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