Category: GCSE Physics

Star is Caught Devouring a Planet

Star is caught devouring planet (from the BBC)

Artist's impression of a planet's destruction

Astronomers have found evidence for a planet being devoured by its star, yielding insights into the fate that will befall Earth in billions of years.

The team uncovered the signature of a planet that had been “eaten” by looking at the chemistry of the host star.

They also think a surviving planet around this star may have been kicked into its unusual orbit by the destruction of a neighbouring world.

Details of the work have been published in Astrophysical Journal Letters.

The US-Polish-Spanish team made the discovery when they were studying the star BD+48 740 – which is one of a stellar class known as red giants. Their observations were made with the Hobby Eberly telescope, based at the McDonald Observatory in Texas.

Rising temperatures near the cores of red giants cause these elderly stars to expand in size, a process which will cause any nearbyHobby-Eberly telescope planets to be destroyed.

“A similar fate may await the inner planets in our solar system, when the Sun becomes a red giant and expands all the way out to Earth’s orbit some five billion years from now,” said co-author Prof Alexander Wolszczan from Pennsylvania State University in the US.

Lithium boost

The first piece of evidence for the missing planet comes from the star’s peculiar chemical composition.

Spectroscopic analysis of BD+48 740 revealed that it contained an abnormally high amount of lithium, a rare element created primarily during the Big Bang 14 billion years ago.

 The discovery was made using the Hobby-Eberly telescope in Texas

Lithium is easily destroyed in stars, so its high abundance in this ageing star is very unusual.

“Theorists have identified only a few, very specific circumstances, other than the Big Bang, under which lithium can be created in stars,” Prof Wolszczan explained.

“In the case of BD+48 740, it is probable that the lithium production was triggered by a mass the size of a planet that spiralled into the star and heated it up while the star was digesting it.”

The second piece of evidence discovered by the astronomers is the highly elliptical orbit of a newly discovered planet around the red giant star. The previously undetected world is at least 1.6 times as massive as Jupiter.

Co-author Andrzej Niedzielski of Nicolaus Copernicus University in Torun, Poland, said that orbits as eccentric as this one are uncommon in planetary systems around evolved stars.

“In fact, the BD+48 740 planet’s orbit is the most elliptical one detected so far,” he added.

Because gravitational interactions between planets are often responsible for such peculiar orbits, the astronomers suspect that the dive of the missing planet toward its host star before it became a giant could have given the surviving massive planet a burst of energy.

This boost would have propelled it into its present unusual orbit.

Team member Eva Villaver of the Universidad Autonoma de Madrid in Spain commented: “Catching a planet in the act of being devoured by a star is an almost improbable feat to accomplish because of the comparative swiftness of the process, but the occurrence of such a collision can be deduced from the way it affects the stellar chemistry.

“The highly elongated orbit of the massive planet we discovered around this lithium-polluted red giant star is exactly the kind of evidence that would point to the star’s recent destruction of its now-missing planet.”

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‘Leap second’ lengthens weekend

‘Leap second’ Lengthens Weekend  (30th Jun 2012)

Wait a second: on Saturday night atomic clocks will read 23 hours, 59 minutes and 60 seconds.

The world is about to get a well-earned long weekend but don’t make big plans because it will only last an extra second. A so-called “leap second” will be added to the world’s atomic clocks as they undergo a rare adjustment to keep them in step with the slowing rotation of the Earth.

To achieve the adjustment, on Saturday night atomic clocks will read 23 hours, 59 minutes and 60 seconds before moving on to midnight Greenwich Mean Time.

Super-accurate atomic clocks are the ultimate reference point by which the world sets its wristwatches. But their precise regularity – which is much more constant than the shifting movement of the Earth around the sun that marks out our days and nights – brings problems of its own.

If no adjustments were made, the clocks would move further ahead and after many years the sun would set at midday. Leap seconds perform a similar function to the extra day in each leap year which keeps the calendar in sync with the seasons. The International Earth Rotation and Reference Systems Service (IERS) based in Paris, is responsible for keeping track of the gap between atomic and planetary time and issuing international edicts on the addition of leap seconds.

“We want to have both times close together and it’s not possible to adjust the Earth’s rotation,” Daniel Gambis, head of the Earth Orientation Centre of the IERS, told Reuters.

Gambis said the turning of the Earth and its movement around the sun were far from constant.

In recent years, a leap second has been added every few years, slightly more infrequent than in the 1970s, despite the long-term slowdown in the Earth’s rotation caused by tides, earthquakes and a host of other natural phenomena.

Adjustments to atomic clocks are more than a technical curiosity.

A collection of the highly accurate devices are used to set Coordinated Universal Time, which governs time standards on the worldwide web, satellite navigation, banking computer networks and international air traffic systems.

There have been calls to abandon leap seconds but a meeting of the International Telecommunications Union (ITU), the UN agency responsible for international communications standards, failed to reach a consensus in January.

“They decided not to decide anything,” said Gambis, adding that another attempt would be made in 2015.

Opponents of the leap second want a simpler system that avoids the costs and margin for error in making manual changes to thousands of computer networks. Supporters argue it needs to stay to preserve the precision of systems in areas such as navigation.

Britain’s Royal Astronomical Society (RAS) says the leap second should be retained until there is a much broader debate on the change.

“This is something that affects not just the telecom industry,” said RAS spokesman Robert Massey. “It would decouple timekeeping from the position of the sun in the sky and so a broad debate is needed.”

Time standards are important in professional astronomy for pointing telescopes in the right direction but critical systems in other areas, not least defence, would also be affected by the change. “To argue that it would be pain-free is not quite true,” Massey said.

In the meantime, Massey plans to use his extra second wisely this weekend. “I’ll enjoy it with an extra second in bed,” he said.

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Dark matter tracks could give earliest view of Universe

Researchers have come up with a way to glimpse the infant Universe by decoding the earliest ripples in its light.

They say this can be achieved by capturing the specific radio wavelength of 21cm from the heavens.

The trick is to tell the difference between 21cm waves from our galaxy and those from distant, ancient sources.

The fact that “dark matter” moved faster than normal matter in the early Universe should help amplify the distant signal, they report in Nature.

That could yield a look at the Universe when it was just 1% of its current age.

The scientists first revealed their 3-D computer simulations on Monday at the Gamma Ray Bursts in the Era of Rapid Follow-up conference, hosted by Liverpool John Moores University.

The current record-holder for the oldest object ever spotted is a galaxy named UDFy-38135539, seen in an optical image captured by the Hubble telescope. Its light escaped more than 13 billion years ago, when the Universe was already a youth of less than 700 million years.

Continue reading the main story

What is redshift?

Diagram of Doppler shift

  • The term “redshift” arises from the fact that light from more distant objects shows up on Earth more red than when it left its source
  • The colour shift comes about because of the Doppler effect, which acts to “stretch” or “compress” waves from moving objects
  • It is at work in the sound of a moving siren: an approaching siren sounds higher-pitched and a receding one sounds lower-pitched
  • In the case of light, approaching objects appear more blue and receding objects appear more red
  • The expansion of the Universe is accelerating, so in general, more distant objects are moving away from us (and each other, and everything else) more quickly than nearer ones
  • At cosmic distances, the shift can profoundly affect the colour – the factor by which the wavelength is “stretched” is called the redshift

Scientists measure these literally astronomical distances with the “redshift” of a given light source; it is a measure of how much the source’s light is stretched as it races away from us in the ever-expanding Universe.

UDFy-38135539 has a redshift of 8.55, but the new work shows promise for looking at stars and galaxies at a redshift of 20.

However, if it works, the view will be a statistical one – astronomers will not actually see individual stars and galaxies, but rather be able to estimate how many objects of what sizes were around in those early days.

But instead of seeing only the largest and brightest objects, as studies with telescopes such as Hubble typically do, it should work down to galactic haloes as small as a millionth the mass of the Milky Way’s halo.

“It’s very small galaxies from very far away; it’s completely hopeless to see them individually with any telescope in the next few decades,” said Rennan Barkana of Tel Aviv University, a co-author on the study.

“That’s why this is so interesting – it’s an indirect detection of the whole population of these galaxies, but it would be a very clear confirmation that these galaxies are there,” Prof Barkana told BBC News.

Dark materials

The 21cm wavelength arises from changes within the atoms of hydrogen, the Universe’s most abundant element, and one that can tell us much about the early Universe before heavier elements were formed.

A key insight lies in the different speed limits for dark matter and normal matter in the early Universe, first pointed out in a 2010 Physical Review D paper.

The early Universe was shaped in part by pressure waves – just like sound waves – created in the wake of the Big Bang. Like air molecules shifted around by sounds, these waves carried and distributed normal matter in regular patterns we can now observe.

Murchison Widefield Array Low-frequency radio telescopes such as the Murchison array could help spot the 21cm waves

But dark matter, because it does not interact with normal matter, was not swayed by the waves, responding only to gravity.

The distributions of dark and normal matter in the early Universe changes just where the matter – mostly hydrogen – ended up, in turn changing where the 21cm emission should come from, and how intense it should be.

Averaged over the sky, there should be a greater variation in this signal than we see locally, and the new paper makes the case that heating by X-ray radiation in those early days should make this statistical fluctuation even easier to spot.

Prof Barkana said that although there are no current radio telescope arrays designed to catch these 21cm waves, several are under construction that could be put onto the task.

“This whole subject of 21cm cosmology is about to open up; there are at least four different groups building radio telescope arrays focussing on about redshift 10,” he said.

“But until now no one has had the incentive to build an array optimised for this (redshift 20) wavelength range.”

By Jason Palmer Science and technology reporter, BBC News

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