A black hole shreds a star, and a bright flare is formed - Video

Computer simulation of the disruption of a star by a black hole shows the formation of an "accretion disk" of stellar material spiraling into the black hole. 

This image shows an early stage in the formation of the disk. 

Credit: James Guillochon

Ramirez-Ruiz, a professor of astronomy and astrophysics at the University of California, Santa Cruz, uses computer simulations to explore the universe's most violent events, so when the first detailed observations of a star being ripped apart by a black hole were reported in 2012 (Gezari et al., Nature), he was eager to compare the data with his simulations.

Ramirez-Ruiz

He was also highly skeptical of one of the published conclusions: that the disrupted star was a rare helium star.

"I was sure it was a normal hydrogen star and we were just not understanding what's going on," said Ramirez-Ruiz.

In a paper accepted for publication in the Astrophysical Journal and available online at arXiv.org, Ramirez-Ruiz and his students explain what happens during the disruption of a normal sun-like star by a supermassive black hole, and they show why observers might fail to see evidence of the hydrogen in the star.


First author and UCSC graduate student James Guillochon (now an Einstein Fellow at Harvard University) and undergraduate Haik Manukian worked with Ramirez-Ruiz to run a series of detailed computer simulations of encounters between stars and black holes.

James Guillochon

Supermassive black holes are thought to lurk at the centers of most galaxies. Some (known as active galactic nuclei) are very bright, emitting intense radiation from superheated gas falling into the black hole.

But the central black holes of most galaxies in the local universe have run out of gas and are quiescent.

Only when an unlucky star approaches too close and gets shredded by the black hole's powerful tidal forces does the galactic center emit a bright flare of light.

Astronomers call this a "tidal disruption event" (TDE), and in a typical galaxy it happens about once every 10,000 years.

"That means you have to survey the nearest 10,000 galaxies in order to see one event, so for many years this was very much a theoretical field," Ramirez-Ruiz said.

Then came Pan-STARRS (Panoramic Survey Telescope and Rapid Response System), which is surveying the sky on a continual basis and has begun detecting and recording observations of these very rare events.

The first one, known as PS1-10jh, was detected in 2010 and published in 2012.

Astronomers recorded the light curve (the rise and fall in brightness over time) and took a spectrum at peak brightness to study the different wavelengths of light.

The spectrum of an active galactic nucleus (AGN) shows characteristic "emission lines" at specific wavelengths corresponding to the most common elements such as hydrogen and helium.

These emission lines appear as spikes of increased intensity in a continuous spectrum. The shocking thing about PS1-10jh was the absence of a hydrogen line in the spectrum.

"It's very unusual to have seen helium and not hydrogen. Stars are mainly made of hydrogen, and stars made only of helium are extremely rare, so this was a huge issue," Guillochon said.

"People said maybe it was a giant star with a helium core and a hydrogen envelope, and the black hole removed the hydrogen first and then the helium core in a second pass."

Guillochon began to explore the possibilities using computer simulations. The results provide a new understanding of the origin of the emission lines in a tidal disruption event.

They show that the flare of light from a tidal disruption contains information about the type of star and the size of the black hole, and they show that PS1-10jh involved the most common type of star (a main-sequence star much like our sun) and a relatively small supermassive black hole.

More Information: 'PS1-10jh: The Disruption of a Main-Sequence Star of Near-Solar Composition': James Guillochon, Haik Manukian, Enrico Ramirez-Ruiz (UC Santa Cruz) arXiv:1304.6397 [astro-ph.HE] (or arXiv:1304.6397v2 [astro-ph.HE])

Spanish Research: Black hole that doesn't emit x-rays discovered near massive star

Trailed intensity image of the two lines constructed from the phase binned spectra. 

Two orbital cycles are displayed for clarity. 

The colour scale indicates counts normalised to the continuum, with the black colour corresponding to 0.98 and the white colour to 1.08 in Fe II and 1.16 in HeII. 

Credit: Nature 

Researchers in Instituto de Astrofísica de Canarias, Universidad de Alicante, Universitat de Barcelona, and Institut de Ciències de l’Espai (IEEC-CSIC), Spain have discovered a black hole that doesn't reveal itself through x-ray radiation thrown off by material that is being sucked into it.

In their paper published in the journal Nature, team members from several research institutions throughout Spain, report that the black hole appears to exist as a companion (binary) to a massive Be star that spins so fast it's surrounded by a gas disk.

I. Negueruela

Up until now, virtually all black holes have been discovered via x-ray radiation signals—as material is pulled in past the point of no return, radiation is flung out into space where it is noted by space scientists here on Earth.

In this new effort, the research team was able to identify the black hole because of its behaviour, rather than its signature.

Many Be stars have been found to have companions—most of the time they are supernova remnants (neutron stars) but never before has a Be star been found to have a black hole as a companion.

The star, named MWC 656 is really big—approximately 10 to 16 times as massive as our sun. It spins really fast too (approximately 671,000 mph) which the researchers say, explains why the black hole next to it doesn't emit any radiation.

J. Casares

They suggest that because the star is spinning so fast, it casts gas into a disk surrounding its equator which in turn is cast off towards the black hole, but rather than being pulled in, the gas joins an accretion disk that surrounds the "mouth" of the black hole, moving so fast (due to the angular momentum of the gas cast off from the star) that it can't be pulled in. Thus the disk simply continues to grow larger.

The black hole is pretty big too (approximately 3.8 to 6.9 more massive than our sun) which likely puts it in the category of stellar mass black holes—those that come into existence when a star runs out of fuel.

The discovery of the "silent" black hole suggests that many more like it might exist, which will undoubtedly lead researchers to look for more, now that they know what to look for.

More information: A Be-type star with a black-hole companion, Nature 505, 378–381 (16 January 2014) J. Casares, I. Negueruela, M. Ribó, I. Ribas, J. M. Paredes, A. Herrero & S. Simón-Díaz DOI: 10.1038/nature12916

NASA Chandra: Star Consumed by Medium-Sized Black Hole | Video

Just a few hundred thousand times our Sun's mass, the hungry singularity in dwarf galaxy 47 Abell 1795 munched on a nearby star for at least 6 years, while the Chandra X-ray Observatory watched. Credit: NASA/CXC/A. Hobart

Newly discovered celestial object defies categories

This is an image of the ROXs 42B system obtained with the Keck telescope. 

The star is located in the center of the masked region. 

ROXs 42Bb orbits at about 150 astronomical units (AU). 

(1 AU=the distance from Earth to the Sun.) 

The other object ("c") is a likely unrelated background star. 

Credit: Thayne Currie

An object discovered by astrophysicists at the University of Toronto (U of T) nearly 500 light years away from the Sun may challenge traditional understandings about how planets and stars form.

The object is located near and likely orbiting a very young star about 440 light years away from the Sun, and is leading astrophysicists to believe that there is not an easy-to-define line between what is and is not a planet.

Thayne Currie

"We have very detailed measurements of this object spanning seven years, even a spectrum revealing its gravity, temperature, and molecular composition. Still, we can't yet determine whether it is a planet or a failed star – what we call a 'brown dwarf'. Depending on what measurement you consider, the answer could be either," said Thayne Currie, a post-doctoral fellow in U of T's Department of Astronomy & Astrophysics and lead author of a report on the discovery published this week in Astrophysical Journal Letters.

Named ROXs 42Bb for it's proximity to the star ROXs 42B, the object is approximately nine times the mass of Jupiter, below the limit most astronomers use to separate planets from brown dwarfs, which are more massive.

However, it is located 30 times further away from the star than Jupiter is from the Sun.

"This situation is a little bit different than deciding if Pluto is a planet. For Pluto, it is whether an object of such low mass amongst a group of similar objects is a planet," said Currie.

"Here, it is whether an object so massive yet so far from its host star is a planet. If so, how did it form?"

Most astronomers believe that gas giant planets like Jupiter and Saturn formed by core accretion, whereby the planets form from a solid core that then accretes a massive gaseous envelope.

Core accretion operates most efficiently closer to the parent star due to the length of time required to first form the core.

An alternate theory proposed for forming gas giant planets is disk instability – a process by which a fragment of a disk gas surrounding a young star directly collapses under its own gravity into a planet. This mechanism works best farther away from the parent star.

More information: The discovery is reported in a study titled "Direct imaging and spectroscopy of a candidate companion below/near the deuterium-burning limit in the young binary star system, ROXs 42B" which can also be viewed on arXiv.org at arxiv.org/abs/1310.4825.

Currie will present these and other findings at the annual meeting of the American Astronomical Society in Washington, DC this week.

Strange solitary planet without companion star in Milky Way

Artist's conception of PSO J318.5-22. Credit: MPIA/V. Ch. Quetz

An international team of astronomers has discovered an exotic young planet that is not orbiting a star.

This free-floating planet, dubbed PSO J318.5-22, is just 80 light-years away from Earth and has a mass only six times that of Jupiter.

The planet formed a mere 12 million years ago—a newborn in planet lifetimes.

It was identified from its faint and unique heat signature by the Pan-STARRS 1 (PS1) wide-field survey telescope on Haleakala, Maui.

Follow-up observations using other telescopes in Hawaii show that it has properties similar to those of gas-giant planets found orbiting around young stars. And yet PSO J318.5-22 is all by itself, without a host star.

"We have never before seen an object free-floating in space that that looks like this.

Michael Liu

It has all the characteristics of young planets found around other stars, but it is drifting out there all alone," explained team leader Dr. Michael Liu of the Institute for Astronomy at the University of Hawaii at Manoa.

"I had often wondered if such solitary objects exist, and now we know they do."

During the past decade, extrasolar planets have been discovered at an incredible pace, with about a thousand found by indirect methods such as wobbling or dimming of their host stars induced by the planet.

However, only a handful of planets have been directly imaged, all of which are around young stars (less than 200 million years old).

PSO J318.5-22 is one of the lowest-mass free-floating objects known, perhaps the very lowest. But its most unique aspect is its similar mass, color, and energy output to directly imaged planets.

"Planets found by direct imaging are incredibly hard to study, since they are right next to their much brighter host stars. PSO J318.5-22 is not orbiting a star so it will be much easier for us to study.

It is going to provide a wonderful view into the inner workings of gas-giant planets like Jupiter shortly after their birth," said Dr. Niall Deacon of the Max Planck Institute for Astronomy in Germany and a co-author of the study.

More information: The discovery paper of PSO J318.5-22 is being published by Astrophysical Journal Letters and is available at arxiv.org/abs/1310.0457

Exoplanet Orbits its star in 8.5 hours

Credit: CRISTINA SANCHIS OJEDA

In the time it takes you to complete a single workday, or get a full night's sleep, a small fireball of a planet 700 light-years away has already completed an entire year.

Researchers at MIT have discovered an Earth-sized exoplanet named Kepler 78b that whips around its host star in a mere 8.5 hours—one of the shortest orbital periods ever detected.

The planet is extremely close to its star—its orbital radius is only about three times the radius of the star—and the scientists have estimated that its surface temperatures may be as high as 3,000 degrees Kelvin, or more than 5,000 degrees Fahrenheit.

In such a scorching environment, the top layer of the planet is likely completely melted, creating a massive, roiling ocean of lava.

What's most exciting to scientists is that they were able to detect light emitted by the planet—the first time that researchers have been able to do so for an exoplanet as small as Kepler 78b.

This light, once analyzed with larger telescopes, may give scientists detailed information about the planet's surface composition and reflective properties.

Kepler 78b is so close to its star that scientists hope to measure its gravitational influence on the star.

Such information may be used to measure the planet's mass, which could make Kepler 78b the first Earth-sized planet outside our own solar system whose mass is known.

The researchers reported their discovery of Kepler 78b in The Astrophysical Journal.

In a separate paper, published in Astrophysical Journal Letters, members of that same group, along with others at MIT and elsewhere, observed KOI 1843.03, a previously discovered exoplanet with an even shorter orbital period: just 4 1/4 hours.

Saul Rappaport

The group, led by physics professor emeritus Saul Rappaport, determined that in order for the planet to maintain its extremely tight orbit around its star, it would have to be incredibly dense, made almost entirely of iron—otherwise, the immense tidal forces from the nearby star would rip the planet to pieces.

"Just the fact that it's able to survive there implies that it's very dense," says Josh Winn, an associate professor of physics at MIT, and co-author on both papers.

"Whether nature actually makes planets that are dense enough to survive even closer in, that's an open question, and would be even more amazing."

Cosmic turbulences result in Star and Black Hole formation

This image shows an artist's rendering of a protoplanetary disc. Credit: Pat Rawlings / NASA

Just how stars and black holes in the Universe are able to form from rotating matter is one of the big questions of astrophysics.

What we do know is that magnetic fields figure prominently into the picture.

However, our current understanding is that they only work if matter is electrically well conductive—but in rotating discs this isn't always the case.

Now, a new publication by Helmholtz-Zentrum Dresden-Rossendorf physicists in the scientific journal Physical Review Letters shows how magnetic fields can also cause turbulences within "dead zones," thus making an important contribution to our current understanding of just how compact objects form in the cosmos.

When Johannes Kepler first proposed his laws of planetary motion in the early days of the 17th century, he could not have foreseen the central role cosmic magnetic fields would play in planetary system formation.

Today, we know that in the absence of magnetic fields, mass would not be able to concentrate in compact bodies like stars and black holes.

One prominent example is our solar system, which formed 4.6 billion years ago through the collapse of a gigantic cloud of gas, whose gravitational pull concentrated particles in its center, culminating in the formation of a large disc.

Dr. Frank Stefani

"These accretion discs are extremely stable from a hydrodynamic perspective as according to Kepler's laws of planetary motion angular momentum increases from the center towards the periphery," explains HZDR's own Dr. Frank Stefani.

"To explain the growth rates of stars and black holes, there has to exist a mechanism, which acts to destabilize the rotating disc and which at the same time ensures mass is transported towards the center and angular momentum towards the periphery."

As early as 1959, Evgenij Velikhov conjectured that magnetic fields are capable of prompting turbulences within stable rotating flows.

Although it wasn't until 1991 that astrophysicists Steven Balbus and John Hawley fully grasped the fundamental significance of this magneto rotational instability (MRI) in cosmic structure formation.

Balbus and Hawley will be this year's recipients of the one million Dollar Shaw Prize for astronomy, which will be given in September 2013.

However, to ensure the MRI actually works, the discs have to exhibit a minimum degree of electrical conductivity.

In areas of low conductivity like the "dead zones" of protoplanetary discs or the far-off regions of accretion discs that surround supermassive black holes, the MRI's effect is numerically difficult to comprehend and is thus a matter of dispute.

HZDR scientists, who to date have been mostly concerned with an experimental study of the MRI, have now offered a new theoretical explanation for this phenomenon.

Read the full article here

More information: O.N. Kirillov, F. Stefani: Extending the range of the inductionless magnetorotational instability, in Physical Review Letters 111 (2013), S. 061103, DOI-Link: link.aps.org/doi/10.1103/PhysRevLett.111.061103

New Star's 'Snow Line' Reveals Clues About Planet Formation

Astronomers have identified the point where carbon monoxide (CO) freezes in the disk around a sunlike star — information that could help them understand how planets form.

A team of international scientists has calculated the CO "snow line" for a star called TW Hydrae, determining that the gas solidifies at about the distance of the orbit of Neptune, where it could help feed the formation of the outer edges of the system.

"The CO snow line is interesting, not only because CO is abundant in the disks, but its snow line is the most accessible to direct observations due to its low freeze-out temperature — it's farther away from the star," said principal investigator Chunhua Qi of the Harvard-Smithsonian Center for Astrophysics.

"It could mark the starting point where smaller icy bodies, like comets, and dwarf planets, like Pluto, would begin to form."

Volatiles like carbon monoxide freeze at a range of temperatures, and each can have its own impact on the growth of orbiting bodies.

The location of the snow lines for volatiles can affect planetary formation. 

Recent research has indicated the water snow line, shown here, lies farther out than previously suspected.

Credit: NASA, ESA, and A. Feild (STScI)

Tracer ions
Stars form when a disk of dust and gas collapses in on itself due to gravity. The remaining material continues to orbit the newly formed object in a disk of material.

As dust and gas particles pass through the disk, scientists say, they come together to form larger and larger clumps that can eventually grow into planets. Frozen volatiles help this process along.

"The snow line provides more sticky solid grains, and enhances the planet formation efficiency and grain growth," Qi told reporters.

But determining the location of these grains can be a challenge. Emission from volatiles along the outside of the disk can make it difficult for scientists to image the telltale signs of frozen compounds.

To locate the region of the disk where CO freezes, Qi and his team utilized a new technique. Using the Atacama Large Millimeter Array (ALMA) in Chile, they searched for the ion diazenylium (N2H+), rather than the hard-to-find carbon monoxide, around TW Hydrae, which lies 176 light-years from Earth.

"N2H+ is easily destroyed in the presence of CO gas, and is abundant where CO has frozen out," Qi said.

The new technique should be helpful for studying the CO snow lines of other stars, which will provide more insight into how outer solar-system objects form.

"As long as the disk is gas-rich, so that there should be enough N2H+, we can use this ion to image the CO snow line," Qi said.

Methuselah: Oldest Known Star HD 140283

Credit: Digitized Sky Survey (DSS), STScI/AURA, Palomar/Caltech, and UKSTU/AAO

This Digitized Sky Survey image shows the oldest star with a well-determined age in our galaxy. Called the Methuselah star, HD 140283 is 190.1 light-years away. 

Astronomers refined the star's age to about 14.5 billion years (which is older than the universe), plus or minus 800 million years. 

Image released March 7, 2013.

Because the aging star is relatively nearby, familiar stars and constellations as seen from Earth are in the sky, but in different locations, as seen in this annotated view.

At upper left is the constellation Orion, which looks distorted from our new perspective in space. 

Just to the upper left of the foreground star is the Pleiades cluster. 

To the lower left of the cluster, our Sun has dimmed to an apparent magnitude of +7, placing it below naked-eye visibility.

ROCOSMOS Soyuz: A Star is launched

Sarah Brightman once sang about losing her heart to a starship trooper. Now she’s paying more than £30million to become one herself – or at least as near as it’s possible for an earthly tourist to get.

The former wife of composer Andrew Lloyd Weber has confirmed she will be travelling to the International Space Station with the Russian Space Agency, ROSCOSMOS.

Reports in the US said she had ‘bumped’ an astronaut off the next flight after outbidding Nasa to secure her seat as the next space tourist.

The 52-year-old singer refused to say how much she paid for her place aboard the Soyuz spacecraft, but said she was getting sponsorship.

A US TV station said she had paid $51million (around £31.8million) – the highest sum ever offered for a ticket.

Miss Brightman will begin training for the mission in 2014 after a 12-month world tour and will lift off later that year for two weeks orbiting Earth.

 She said: ‘I am more excited about this than I have been about anything I have done. ‘Most of my life I have felt an incredible desire to take the journey to space that I have now begun. This is beyond my wildest dreams.'

She has already undergone physical and psychological tests in Moscow to prove she is fit enough for the challenge. ‘I was prodded and poked and a lot of blood was taken,’ she said.

nited Kingdom Infrared Telescope (UKIRT): Mysteries Of Massive Star Formation

A false colour image of a massive star forming region shows outflows associated with IRAS 05137+3919. The image is constructed from J (1.25 micron, blue), H (1.65 micron, green) and H2 (2.122 micron, red). The shocked regions of the outflows rich in line emission appear red here. The blue objects are mostly foreground stars. IRAS 05137+3919 is a luminous Young Stellor Object (YSO) of late-O spectral type. We detect two bipolar outflows here, emanating from the central double star. Credit: JAC/UKIRT.

Using the United Kingdom Infrared Telescope (UKIRT) astronomers have found the leading mechanism by which most of the massive stars form in our Galaxy.

The largest near-infrared survey of massive star forming regions to date has revealed that a major fraction of these massive stars form by collecting matter onto disks around their equatorial regions.

This was revealed by the detection of gas outflows and shocked regions associated with massive young stars in formation, located in clouds of gas and dust in our Galaxy.

The survey was carried out by a team lead by Dr. Watson Varricatt from the Joint Astronomy Centre and included Dr. Chris Davis (Joint Astronomy Centre), Dr. Suzanne Ramsay (ESO, Germany) and Dr. Stephen Todd (UKATC, Edinburgh, UK).

We know that lower-mass stars like our Sun form by gravitational collapse of material inside clouds of gas and dust in space.

The gas and dust spiral down onto the equatorial regions of the young star via a process known as accretion.

At the same time these accreting young stars drive high velocity jets of gas outwards at thousands of miles per hour.

These "outflows" radiate at infrared wavelengths (this emission is actually produced by hydrogen molecules heated to thousands of degrees). Consequently, observations in the infrared can be used to search for not only the youngest stars, but also evidence of the accretion process.

The big question is, do the massive stars form the same way, or do they form using a different process?

For massive stars, with masses larger than 10 times the mass of our Sun, it has been proposed that the extreme energy output of these young stars, which start nuclear burning in their cores even before they complete their growth through accretion, will prevent further growth by blowing away the accretion disks.

Hence, alternate scenarios like mergers of lower mass stars have been suggested as the main mechanism for massive star formation.

The presence or absence of outflows from massive young stars will tell us whether accretion or some other methods lead to their formation.

ESA Herschel Images: hidden side of star birth

ESA - Herschel reveals the hidden side of star birth

RCW 120 is a galactic bubble with a large surprise. How large? At least 8 times the mass of the Sun. Nestled in the shell around this large bubble is an embryonic star that looks set to turn into one of the brightest stars in the Galaxy.

The Galactic bubble is known as RCW 120. It lies about 4300 light-years away and has been formed by a star at its centre. The star is not visible at these infrared wavelengths but pushes on the surrounding dust and gas with nothing more than the power of its starlight.

In the 2.5 million years the star has existed. It has raised the density of matter in the bubble wall so much that the quantity trapped there can now collapse to form new stars.

The bright knot to the right of the base of the bubble is an unexpectedly large, embryonic star, triggered into formation by the power of the central star.

Herschel’s observations have shown that it already contains between 8-10 times the mass of our Sun. The star can only get bigger because it is surrounded by a cloud containing an additional 2000 solar masses.

Not all of that will fall onto the star, even the largest stars in the Galaxy do not exceed 150 solar masses but the question of what stops the matter falling onto the star is a puzzle for modern astronomers.

According to theory, stars should stop forming at about 8 solar masses. At that mass they should become so hot that they shine powerfully at ultraviolet wavelengths.

This light should push the surrounding matter away, much as the central star did to form this bubble. But clearly sometimes this mass limit is exceeded otherwise there would be no giant stars in the Galaxy.

So astronomers would like to know how some stars can seem to defy physics and grow so large. Is this newly discovered stellar embryo destined to grow into a stellar monster? At the moment, nobody knows but further analysis of this Herschel image could give us invaluable clues.

Credits: ESA/PACS/SPIRE/HOBYS Consortia

Distant Star Factory

Arp 220 is a nearby example of a merged starburst galaxy similar to SMM J2135-0102. Located 250 million light-years from Earth, Arp 220 is the aftermath of a collision between two spiral galaxies. The collision, which began about 700 million years ago, has sparked a crackling burst of star formation, resulting in about 200 huge star clusters in a packed, dusty region about 5,000 light-years across (about 5 percent of the Milky Way's diameter). The star clusters are the bluish-white bright knots visible in the Hubble image. Credit: NASA, ESA, the Hubble Heritage-ESA/Hubble Collaboration, and A. Evans (UVa/NRAO/Stony Brook)

Astronomers have combined a natural gravitational lens and a sophisticated telescope array to get the sharpest view ever of "star factories" in a galaxy over 10 billion light-years from Earth. They found that the distant galaxy, known as SMM J2135-0102, is making new stars 250 times faster than our Galaxy, the Milky Way.

They also pinpointed four discrete star-forming regions within the galaxy, each over 100 times brighter than locations (like the Orion Nebula) where stars form in our Galaxy. This is the first time that astronomers have been able to study properties of individual star-forming regions within a galaxy so far from Earth.

Read the full article here

An Orange Dwarf Star is hurtling Towards us

A star is hurtling towards us. It will almost certainly clip the outskirts of the solar system and send comets towards Earth – though not for a while.

Vadim Bobylev of the Pulkovo Observatory in St Petersburg, Russia, modelled the paths of neighbouring stars using data from the European Space Agency's Hipparcos satellite and from ground-based measurements of the speeds of stars.

He found four previously unidentified stars that will pass within roughly 9.5 light years of Earth. They will tug on the Oort cloud, a diffuse cloud of icy objects around the solar system thought to be a reservoir of comets.

Orange danger
However, the biggest threat comes from another star, Gliese 710, an orange dwarf now some 63 light years away but zooming our way at 14 kilometres per second. Previous studies have suggested that Gliese 710 could pass through the Oort cloud in about 1.5million years.

Bobylev's calculations suggest Gliese 710 has an 86 per cent chance of passing through the Oort cloud. This could scatter millions of comets into paths that cross Earth's orbit. Fortunately, previous work on the effect of a star tangling with the Oort cloud hints the comets would arrive in a trickle, with only one entering an Earth-crossing orbit per year.

Neptune tweak
Gliese 710 also has a 1 in 10,000 probability of coming within 1000 astronomical units – 1 AU being the distance from the Earth to the sun. Such a path could jostle objects in the Oort cloud, the Kuiper belt – a swarm of icy objects beyond Neptune's orbit – as well as others that orbit in a disc between the two regions.

The star could also change Neptune's orbit a fraction, says Paul Weissman of NASA's Jet Propulsion Laboratory in Pasadena, California. "It would be a very significant event."

Although an encounter with Gliese 710 was already thought possible, "it's nice to see it confirmed with a better model and better data", says Weissman. "It's a solid piece of work."

Journal reference: Astronomy Letters, vol 36, p 230

Watching a 1a Supernova Explosion: Star Destruction

(Image: Argonne National Laboratory)
Visualisation of an exploding supernova. More Simulator Pictures here

The explosion itself is over in less than 5 seconds, but the supercomputer uses more than 160,000 processors, and expends 22 million computational hours, simulating it.

Cosmic spokes and pummelled planets: 1,000 Years Old

The explosion of a massive star more than 1000 years ago created this colourful remnant, called E0102. It sits some 190,000 light years away in a nearby galaxy called the Small Magellanic Cloud.

The ejected remains seem to form a cylinder that we see end-on. The highest-energy X-rays are shown in blue, and the lowest in orange. A star not visible in this image is responsible for illuminating the green cloud of gas and dust on the lower right.

This image is a composite taken by the Hubble Space Telescope and the orbiting Chandra X-ray Observatory, in celebration of the 10th anniversary of Chandra's deployment after launching into space aboard the space shuttle Columbia.

(Image: X-ray: NASA/CXC/MIT/ D. Dewey et al./SAO/J. DePasquale; Optical: NASA/STScI)