RSSAll Entries Tagged With: "Milky Way"

Rogue stars sail in intergalactic space

Animation of a rogue star

Illustration of a rogue star being ejected from the galaxy after tangling with the Milky Way’s central black hole.

IT’S VERY DIFFICULT to knock a star out of our Milky Way galaxy. In fact, the main mechanism that astronomers have come up with that can give a star the three-million-plus kilometre-per-hour kick it takes involves tangling with the supermassive black hole at the Milky Way’s core.

So far astronomers have found 16 of these “hypervelocity” stars. Although they are travelling fast enough to eventually escape galaxy’s gravitational grasp, they have actually been discovered while they are still inside the galaxy.

Now, astronomers report in a recent issue of the Astronomical Journal that they’ve identified a group of more than 675 stars on the outskirts of the Milky Way, which they argue are hypervelocity stars that have been ejected from the galactic core.

They selected these stars based on their location in intergalactic space between the Milky Way and the nearby Andromeda galaxy and by their peculiar red coloration.

“These stars really stand out. They are red giant stars with high metallicity which gives them an unusual colour,” says Vanderbilt University Assistant Professor Kelly Holley-Bockelmann who conducted the study with graduate student Lauren Palladino.

In astronomy and cosmology, “metallicity” is a measure of the proportion of chemical elements other than hydrogen and helium that a star contains. In this case, high metallicity is a signature that indicates an inner galactic origin—older stars and stars from the galactic fringes tend to have lower metallicities.

The researchers identified the candidates by analysing millions of stars catalogued in the Sloan Digital Sky Survey.

Illustration of a supermassive black hole

Illustration of a supermassive black hole, like the one thought to reside at the core of our Milky Way galaxy.

Encounter with a black hole

“We figured that these rogue stars must be there, outside the galaxy, but no one had ever looked for them. So we decided to give it a try,” said Holley-Bockelmann, who is studying the behaviour of the black hole at the centre of the Milky Way galaxy.

Astronomers have now found evidence for giant black holes at the centres of many galaxies. They estimate that the Milky Way’s central black hole has a mass of four million solar masses. They calculate that the gravitational field surrounding such a supermassive black hole is strong enough to accelerate stars to hypervelocities.

The typical scenario involves a binary pair of stars that get caught in the black hole’s grip. As one of the stars spirals in towards the black hole, its companion is flung outward at a tremendous velocity. A second scenario takes place during periods when the central black hole is in the process of ingesting a smaller black hole. Any star that ventures too close to the circling pair can also get a hypervelocity kick.

Even travelling at hypervelocities, it would take a star about 10 million years to travel from the Milky Way’s central hub to its outskirts 50,000 light years away.

Adapted from information issued by Vanderbilt University. Images courtesy Michael Smelzer / Vanderbilt University / Jenni Ohnstad / NASA Jet Propulsion Laboratory.

Get SpaceInfo.com.au daily updates by RSS or email! Click the RSS Feed link at the top right-hand corner of this page, and then save the RSS Feed page to your bookmarks. Or, enter your email address (privacy assured) and we’ll send you daily updates. Or follow us on Twitter, @spaceinfo_oz

Like this story? Please share or recommend it…

Journey to the Centre of the Galaxy

HIDING BEHIND DUST in the direction of the constellations Sagittarius and Scorpius is the centre of our own Milky Way galaxy, over 25,000 light years away. The infrared vision of NASA’s Spitzer Space Telescope and the European Space Agency’s Herschel Space Observatory sees through the dust showing us this strange and tumultuous region.

Adapted from information issued by NASA / JPL-Caltech / ESA.

Get SpaceInfo.com.au daily updates by RSS or email! Click the RSS Feed link at the top right-hand corner of this page, and then save the RSS Feed page to your bookmarks. Or, enter your email address (privacy assured) and we’ll send you daily updates. Or follow us on Twitter, @spaceinfo_oz

Like this story? Please share or recommend it…

Hidden star groups uncovered

Star clusters discovered using VISTA

Using data from the VISTA infrared survey telescope, astronomers have discovered 96 new 'open' star clusters hidden behind dust in the Milky Way, 30 of which are shown in this mosaic.

  • Almost 100 star clusters found hiding behind dust in the Milky Way
  • Uncovered using the dust-penetrating power of infrared
  • There could be 30,000 more clusters still waiting to be found

NINETY-SIX PREVIOUSLY UNKNOWN ‘open star clusters’ have been found hiding behind dust in the Milky Way.

These tiny and faint groupings were invisible to previous surveys, but they could not escape the sensitive infrared detectors VISTA—an infrared survey telescope at the European Southern Observatory’s (ESO) Paranal Observatory in Chile—which can peer through the dust.

This result comes just one year after the start of the VISTA Variables in the Via Lactea programme (VVV), one of the six surveys running on the new telescope. (‘Via Lactea’ is the Latin name for the Milky Way.)

Invisible to most telescopes

Most stars that weigh more than half as much as our Sun form in groups, called open star clusters. These clusters are the building blocks of galaxies and vital for the formation and evolution of galaxies such as our own.

However, stellar clusters form in very dusty regions that absorb most of the visible light that the young stars emit, making them invisible to most telescopes, but not to VISTA.

In order to spot the youngest star clusters, the astronomers concentrated their search towards known star-forming areas. They found that regions that looked empty in previous visible-light surveys, actually held lots of clusters.

VISTA telescope

VISTA is an infrared survey telescope at the European Southern Observatory in Chile.

No wonder they were hidden

By using carefully tuned computer software, the team was able to remove the foreground stars appearing in front of each cluster in order to count the genuine cluster members.

Afterwards, they made visual inspections of the images to measure the cluster sizes, and for the more populous clusters they made other measurements such as distance, and the age of the stars.

“We found that … the dust in front of these clusters makes them appear 10,000 to 100 million times fainter in visible light,” explains Radostin Kurtev, another member of the team. “It’s no wonder they were hidden.”

Tip of the iceberg

Only 2,500 open clusters are known so far in the Milky Way, but astronomers think there might be as many as 30,000 still hiding behind the dust and gas.

These new 96 open clusters might be only the tip of the iceberg.

“We’ve just started to use more sophisticated automatic software to search for less concentrated and older clusters,” adds Jura Borissova, lead author of the study. “I am confident that many more are coming soon.”

Adapted from information issued by ESO. Images courtesy ESO / J. Borissova / Steven Beard (UKATC).

Get SpaceInfo.com.au daily updates by RSS or email! Click the RSS Feed link at the top right-hand corner of this page, and then save the RSS Feed page to your bookmarks. Or, enter your email address (privacy assured) and we’ll send you daily updates. Or follow us on Twitter, @spaceinfo_oz

Like this story? Please share or recommend it…

Billion-pixel space camera

Artist's impression of Gaia

Gaia's billion-pixel digital camera will study a billion stars and other objects in our Milky Way galaxy and other galaxies.

  • Gaia mission set for launch in 2013
  • Will carry a billion-pixel digital camera
  • Will map 1 billion stars in the Milky Way

THE LARGEST DIGITAL CAMERA ever built for a space mission has been painstakingly pieced together from 106 separate electronic detectors. The resulting “billion-pixel array” will serve as the super-sensitive ‘eye’ of the European Space Agency’s (ESA) galaxy-mapping Gaia mission.

While the naked human eye can see several thousand stars on a clear night, Gaia will map a billion stars within our Milky Way galaxy and its neighbouring galaxies over the course of its five-year mission from 2013.

It will chart their brightnesses and spectral characteristics along with their three-dimensional positions and motions.

A key step

In order to detect distant stars up to a million times fainter than the eye can see, Gaia will carry 106 charge coupled devices (CCDs)—advanced versions of the chips found within standard digital cameras.

Developed for the mission by e2v Technologies of Chelmsford, UK, these rectangular detectors are a little smaller than a credit card, each one measuring 4.7 x 6cm but thinner than a human hair.

The 50 x 100cm mosaic has been assembled at the Toulouse facility of Gaia prime contractor, Astrium France.

Technicians working on Gaia’s focal plane

A total of 106 CCDs make up Gaia’s focal plane. Technicians from Astrium France are seen attaching and aligning the CCDs onto the support structure.

Technicians spent much of May carefully fitting together each CCD package on the support structure, leaving only a 1mm gap between them. Working in double shifts in strict cleanroom conditions, they added an average four CCDs per day, finally completing their task on June 1.

“The mounting and precise alignment of the 106 CCDs is a key step in the assembly of the flight model focal plane assembly,” said Philippe Garé, ESA’s Gaia payload manager.

A cool view

The completed array is arranged in seven rows of CCDs. The main part comprises 102 detectors dedicated to star detection, while four others will check the image quality of each telescope and the stability of the 106.5º angle between the two telescopes that Gaia will use to obtain stereo views of stars.

In order to increase the sensitivity of its detectors, the spacecraft will maintain their temperature at a chilly –110ºC. The following video shows how Gaia’s heatshield will unfurl to protect it from the Sun:

Gaia’s CCD support structure, like much of the rest of the spacecraft, is made of silicon carbide (SiC )—a ceramic-like material, extraordinarily resistant to deformation under temperature changes.

First synthesised as a diamond substitute, SiC has the advantage of low weight—the entire support structure with its detectors is only 20 kg.

Targets near and far

Scheduled for launch in 2013, Gaia’s three-dimensional star map will help to reveal the composition, formation and evolution of the Milky Way, sampling 1% of our galaxy’s stars.

Gaia will also study large numbers of other celestial bodies, from minor bodies in our own Solar System to more distant galaxies and quasars near the edge of the observable Universe.

Adapted from information issued by ESA. Images courtesy ESA / Astrium / C. Carreau.

Get SpaceInfo.com.au daily updates by RSS or email! Click the RSS Feed link at the top right-hand corner of this page, and then save the RSS Feed page to your bookmarks. Or, enter your email address (privacy assured) and we’ll send you daily updates. Or follow us on Twitter, @spaceinfo_oz

Like this story? Please share or recommend it…

Milky Way is a galactic cannibal

Galaxy NGC 1300

The barred-spiral galaxy NGC1300 has a "bar" structure—the elongated section through the middle of the galaxy from which the spiral arms extend. The Milky Way is thought to have a bar like this too.

LATEST RESEARCH HAS GIVEN ASTRONOMERS new insight into how our Milky Way galaxy may have formed, including its history of devouring smaller neighbouring galaxies that get too close.

One such incident, the focus of this recent work, could be responsible for the shape of our galaxy.

Astronomer Dr Kenji Bekki of the International Centre for Radio Astronomy Research (ICRAR) in Perth worked with international collaborators to simulate a merger between a smaller galaxy and the infant Milky Way some nine billion years ago.

“Our computer model shows a distinct bar-shape in a portion of our galaxy called the thick disc. If observed, this bar would be clear evidence for a merger taking place in the early history of the Milky Way,” says Dr Bekki, who is based at The University of Western Australia node of ICRAR.

Side-on view of the simulated Milky Way

A side-on view of the simulated Milky Way, showing its different parts—the thin disc in blue and the thick disc in red. The green dot shows the location of the Solar System within the thin disc.

Bar—or elongated—central sections are seen in many galaxies.

The Milky Way is shaped like two fried eggs placed back to back, where the yolks are a puffy collection of older stars called the bulge. The whites are a bright collection of younger stars known as the thin disc. The thick disc is a puffed up version of the thin disc, but is ten times lighter.

Current ideas predict that the thick disc used to be shaped like the thin disc, but was ‘puffed up’ during a merger with a smaller galaxy. The thin disc we observe today was then slowly formed from other material in our galaxy.

The idea that our galaxy was shaped in this way by galactic merging has been around for about 30 years, but until now this hasn’t been directly testable. The new research provides the best avenue yet to determine whether or not the merger actually occurred.

“If our predicted bar-shape is not detected within the thick disc, then we know it can’t have formed as early as we think. We would then need some new ideas for how our galaxy came to look the way it does today,” says Dr Bekki.

“Detecting the shape of the thick disc involves working out the movement of individual stars, a lengthy painstaking process. From our vantage point within the thin disc of the Galaxy, it’s difficult for us to know exactly what shape our Galaxy is,” he adds.

ICRAR is a joint venture between Curtin University and The University of Western Australia providing research excellence in the field of radio astronomy.

The research will be published in the Astrophysical Journal on July 10, 2011.

Adapted from information issued by ICRAR. Images courtesy Dr Kenji Bekki (ICRAR) / Credit: NASA, ESA, and The Hubble Heritage Team STScI/AURA).

Get SpaceInfo.com.au daily updates by RSS or email! Click the RSS Feed link at the top right-hand corner of this page, and then save the RSS Feed page to your bookmarks. Or, enter your email address (privacy assured) and we’ll send you daily updates. Or follow us on Twitter, @spaceinfo_oz

Like this story? Please share or recommend it…

Milky Way spreads its arms

Diagram showing possible new Milky Way spiral arm

The Milky Way's basic structure is believed to involve two main spiral arms emanating from opposite ends of an elongated central section. But only parts of the arms can be seen—grey segments indicate portions not yet detected. (Other known spiral arm segments, including the Sun's own spur, are omitted from this diagram for clarity.)

OUR MILKY WAY GALAXY, like other spiral galaxies, comprises a main flattened body (or “disc”) with sweeping arms of stars, gas, and dust that curve around the galaxy like the arms of a huge pinwheel.

Our Solar System is located in a “spur” or offshoot that lies between two of the spiral arms, collectively orbiting around the galaxy about 25,000 light-years from its centre.

But because the Milky Way contains huge amounts of dust that blocks our view at normal optical wavelengths, it is extremely difficult to gauge the shape of the galaxy from our vantage point within the disc. It’s like trying to determine the overall shape of forest when you’re stuck in the middle.

This means that our knowledge of our galaxy’s spiral arms is much less certain than that of other galaxies such as Andromeda … because even though Andromeda is million light-years away, we have the advantage of seeing it from the outside.

Radio telescopes can peer through the dust, however, and molecules like carbon monoxide that emit radio wavelengths and concentrate in the Milky Way’s spiral arms, are particularly good “tracers” of the arms’ structure.

Using a small 1.2-metre radio telescope on the roof of their science building in Cambridge, Massachusetts, Harvard-Smithsonian Centre for Astrophysics astronomers Tom Dame and Pat Thaddeus used carbon monoxide emission to search for evidence of spiral arms in the most distant parts of the Milky Way, and discovered a large, new spiral arm peppered with dense concentrations of molecular gas.

They suggest that the new spiral is actually the far end of the Scutum-Centaurus Arm, one of the two main spiral arms thought to originate from opposite ends of our galaxy’s central section.

If their findings are confirmed, it will demonstrate that the Milky Way has a striking symmetry, with the new arm being the counterpart of the nearby Perseus Arm.

Adapted from information issued by the Harvard-Smithsonian Centre for Astrophysics. Image courtesy T. Dame.

Get SpaceInfo.com.au daily updates by RSS or email! Click the RSS Feed link at the top right-hand corner of this page, and then save the RSS Feed page to your bookmarks. Or, enter your email address (privacy assured) and we’ll send you daily updates. Or follow us on Twitter, @spaceinfo_oz

Like this story? Please share or recommend it…

How to spot a spinning black hole

Artist's impression of a black hole

Astronomers should be able to detect changes to light passing by the black hole, caused by the black hole's distortion of local space-time. (Artist's impression.)

  • Black holes predicted to cause distortions in nearby space-time
  • Light travelling past a black hole should be changed by the distortion
  • Should be possible to spot the changes using radio telescopes

AN INTERNATIONAL GROUP of astronomers and physicists—including Dr Gabriel Molina-Terriza of Macquarie University in Sydney—has found that spinning black holes should leave an imprint on passing radiation that ought to be detectable using today’s most sensitive radio telescopes.

Observing this signature, they say, could tell us more about how galaxies evolve and provide a further test of Einstein’s general theory of relativity.

General relativity tells us that very massive objects such as black holes warp space-time such that the path of any passing light is bent, an effect known as gravitational lensing.

The theory also predicts that when a black hole rotates it will drag space-time around with it, creating a vortex that constrains all nearby objects, including photons, to follow that rotation.

Astronomers already have evidence that the supermassive black holes believed to lie at the core of many galaxies rotate. However, this evidence is indirect.

The rotation of the Milky Way’s black hole, for example, is suggested by the velocity and movement of nearby stars within the galaxy. But this approach is undermined because we don’t know exactly how much matter, particularly dark matter, the galaxy contains.

Some astronomers think that the Milky Way’s black hole is rotating very quickly while others maintain it is rotating much more slowly.

This video shows the motion of stars around the Milky Way’s black hole. Although the black hole itself cannot be seen, its presence can be inferred from the looping orbits of the stars.

Fundamentally important

In the latest work, Fabrizio Tamburini of the University of Padova in Italy and colleagues instead show how to detect the rotation by measuring changes to the light from a distant star or from the cloud of accumulated material surrounding a black hole.

They point out that the “wavefront” of light travelling in a plane perpendicular to the black hole’s axis of spin will get twisted as it passes close to the black hole, since half of the wave front will be moving in the direction of advancing space-time and the other half in the direction of receding space-time.

In other words, the phase of the radiation emanating from close to a rotating black hole should have a distinctive “signature”.

Image of the Milky Way's centre

View of the central regions of our Milky Way galaxy, at the core of which is believed to live a huge black hole.

The researchers used a computer simulation to model the signature resulting from the rotation of the Milky Way’s black hole and found that this variation ought to be visible from the ground.

They say the way to measure it is to point an array of radio telescopes at the centre of the galaxy, using different telescopes to observe different segments of the approaching wavefront, and then superimpose these segments to calculate their relative phase. This procedure would be repeated, each time with the telescopes pointing to a different section of the tiny patch of sky surrounding the black hole.

Tamburini describes his group’s findings as “fundamentally important”, given, he says, that most massive objects in the universe rotate.

In particular, he believes that studying the rotation of black holes in active galactic nuclei can provide a lot of information about the evolution of these galaxies.

And he maintains that his group could carry out such measurements within two years using an existing array of radio telescopes, such as the Very Long Baseline Array in the US, or the LOIS-LOFAR in Europe, were funding forthcoming.

Adapted from information issued by Macquarie University. Image credits: NASA / ESA / G. Bacon (STScI) / SSC / CXC.

Get SpaceInfo.com.au daily updates by RSS or email! Click the RSS Feed link at the top right-hand corner of this page, and then save the RSS Feed page to your bookmarks. Or, enter your email address (privacy assured) and we’ll send you daily updates. Or follow us on Twitter, @spaceinfo_oz

Aquarius younger by billions of years

Stars in the Milky way

Astronomers have identified a massive swarm of stars within the Milky Way, now known as the Aquarius Stream, that seem to be the remains of a smaller, external galaxy that was destroyed by the Milky Way's gravitational pull.

AN INTERNATIONAL TEAM of astronomers has discovered a new stream of stars in our Milky Way, thanks to data collected at the ANU Siding Spring Observatory.

The research, led by Dr Mary Williams from the Astrophysical Institute Potsdam (AIP), is part of the Radial Velocity Experiment (RAVE) and used data from Siding Spring to measure the velocities of 250,000 stars.

The new ‘Aquarius Stream’ is named after the constellation of Aquarius in which it resides. The stream of stars is a remnant of a smaller galaxy in our cosmic neighbourhood, which was pulled apart by the gravitational pull of the Milky Way about 700 million years ago.

Dr Mary Williams, a former graduate student of the Research School of Astronomy and Astrophysics at ANU, said the Aquarius Stream was particularly hard to find, located deep within the Milky Way where it was indistinguishable from the huge quantity of stars blocking our view of it.

Aquarius Stream map

Astronomers have identified a massive swarm of stars within the Milky Way, now known as the Aquarius Stream, that seem to be the remains of a smaller, external galaxy that was destroyed by the Milky Way's gravitational pull.

“It was right on our doorstep, but we just couldn’t see it,” said Dr Williams.

Dr Williams used the RAVE data to draw conclusions about the formation of the Milky Way.  She said that by astronomical standards, the 700-million-year-old Aquarius stream is exceptionally young. Other known streams of stars located on the outskirts of our galaxy are billions of years old.

Professor Matthias Steinmetz, project leader of the multinational RAVE collaboration at AIP said he is optimistic the method used by Dr Williams and her team will lead to many more discoveries of this kind.

“We want to understand the formation history of our Milky Way,” he said. “We want to find out how frequently constellations have merged with neighbouring galaxies in the past, and how many we are to expect in the future.”

While much about the galaxy surrounding our planet Earth remains unknown, astronomers are certain about one thing—the Milky Way’s next huge collision will be with the Andromeda galaxy. This cosmic collision is predicted to take place in about three billion years—unless one of the dwarf galaxies discovered over the past few years beats Andromeda to it.

This video shows a highly speeded up computer simulation of the collision between the Milky Way and Andromeda. See what happens to the shape of the Milky Way following the collision:

RAVE is a multinational project, involving scientists from Australia, Germany, France, UK, Italy, Canada, the Netherlands, Switzerland, Slovenia and the USA.

Adapted from information issued by ANU. Images courtesy ANU and Hubble Heritage Team (AURA / STScI / NASA / ESA).

Get SpaceInfo.com.au daily updates by RSS or email! Click the RSS Feed link at the top right-hand corner of this page, and then save the RSS Feed page to your bookmarks. Or, enter your email address (privacy assured) and we’ll send you daily updates. Or follow us on Twitter, @spaceinfo_oz

Glimpse of glittering stars and gas

GLIMPSE360 and 2MASS image

Two bright stars illuminate clouds of gas in this false-colour image made from Spitzer Space Telescope GLIMPSE360 and Two Micron All Sky Survey data. The gas is composed of polycyclic aromatic hydrocarbons (PAHs), molecules that on Earth are found in car exhausts and grilled food on BBQs!

  • Spitzer space telescope making Milky Way map
  • Focusing on our galaxy’s outer reaches

NASA’s Spitzer space telescope—which is similar to the Hubble Space Telescope but is optimised to pick up infrared radiation (heat)—is partway through producing a huge map of the outskirts of our Milky Way galaxy.

Our galaxy is made up of a central bulge surrounded by octopus-like spiral arms. The overall shape is that of a disc…round, with a thicker middle and thinner edges.

Our Solar System is located on one of the spiral arms, about two-thirds of the way out from the central bulge.

The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire 360, or GLIMPSE360, is a follow-up to the GLIMPSE and GLIMPSE3D surveys, which focused on the inner parts of our galaxy.

GLIMPSE360 will look outwards to where the Milky Way’s star fields begin to fade out and intergalactic space begins.

“GLIMPSE360 will see to the edge of the Milky Way galaxy better than any telescope has before,” says Barbara Whitney, principal investigator for the survey, Senior Scientist at the University of Wisconsin and a Senior Research Scientist at the Space Science Institute in Boulder, Colorado.

Astronomers don’t know much about the outer limits of the Milky Way, and a number of puzzles remain to be solved.

GLIMPSE360 and 2MASS image

The bubble in the centre of this gas cloud is being "inflated" by strong winds blown from young, hot stars. (False-colour image.)

One of them is how and why stars are born in regions where there is little star-making material—interstellar clouds of gas and dust.

“It’s like looking into the wilderness of our galaxy,” says Whitney. “While mapping the stars and dust out there, we hope to answer some major questions about an environment that is very different from the inner Milky Way.”

Studies of other galaxies have shown that there can be a surprising amount of star formation going on in the outer reaches.

Being an infrared telescope, Spitzer was launched with a cooling system to keep it’s own equipment very cold in order to prevent stray heat from interfering with its observations. But the coolant fluid ran out in early 2009, and the telescope has been operating in “warm mode” ever since. It can’t do quite the same observations as before, but it is still an incredibly capable facility that is in very good technical health.

“We look forward to what GLIMPSE360 will show us,” Whitney says. “The adventure is just getting started.”

Story by Jonathan Nally, Editor, SpaceInfo.com.au

Images courtesy NASA / JPL-Caltech / 2MASS / B. Whitney (SSI/University of Wisconsin).

Get SpaceInfo.com.au daily updates by RSS or email! Click the RSS Feed link at the top right-hand corner of this page, and then save the RSS Feed page to your bookmarks. Or, enter your email address (privacy assured) and we’ll send you daily updates. Or follow us on Twitter, @spaceinfo_oz

Hypervelocity star leaves home

Illustration of a star being ejected from the Milky Way

In this illustration, the hot, blue star HE 0437-5439 has been tossed out of the centre of our Milky Way galaxy with enough speed—2.5 million kilometres per hour—to escape the galaxy's gravitational clutches.

  • Star is moving at 2.5 million kilometres per hour
  • Hubble shows that it originated in the core of the Milky Way
  • Now on the Milky Way’s outskirts and heading outward

Using the Hubble Space Telescope, astronomers have studied a “super-hot blue star” leaving our Milky Way galaxy three times faster than the speed of the Sun.

The “hypervelocity” star—known as HE 0437-5439—is presently 200,000 light-years from the galactic centre, and shooting outward at around 2.5 million kilometres per hour.

It also appears to be bafflingly youthful.

So what’s a nice young star doing in a place like that?

The astronomers say the most likely scenario is that it was once part of a triple-star system that lived in the inner parts of our galaxy, and which one day came too close the Milky Way’s central black hole.

They think one of the stars was captured by the black hole, but that the other two were boosted onto a trajectory that sent them zooming up and out of the Milky Way.

Illustration of a triple-star system being split up by coming too close to a black hole

This illustration shows how a triple-star system could be split up by coming too close to a black hole. One star gets captured, the other two head off together with extra speed. Those two stars then merged to become a single "blue straggler" star.

Somewhere along the way, the two stars merged to form one, much bigger and hotter star.

All of the 16 known hypervelocity stars seem to have come from the Galaxy’s inner region, but HE 0437-5439 is the first to have been pinned down as coming from the galactic core.

“Using Hubble, we can for the first time trace back to where the star came from by measuring the star’s direction of motion on the sky,” said astronomer Warren Brown of the Harvard-Smithsonian Centre for Astrophysics in Cambridge, Massachusetts. “Our measurements point directly to the Milky Way centre.”

An age-old problem

The star’s apparent youth is another puzzle. In 2008, a different team of astronomers found a chemical match between the light spectrum of HE 0437-5439 and stars that live in the Large Magellanic Cloud (LMC), a neighbouring galaxy only 65,000 light-years from HE 0437-5439’s present position.

Hubble image of HE 0437-5439

HE 0437-5439 is 200,000 light-years from the Milky Way's core, heading outward at 2.5 million kilometres per hour.

This implied that HE 0437-5439 might have been travelling in the opposite direction, having come from the LMC.

But using Hubble to measure the star’s movement through space—by comparing images taken 3.5 years apart—it’s now clear that it originated in the inner Milky Way.

At its speed, the star should have taken around 100 million years to reach its current location. But stars this big and hot tend to “burn out” quickly, in perhaps just 20 million years.

So how did it go so far without burning out?

This is where the triple-star origin comes in. With one star captured by the black hole, the other two headed off together at a great rate of knots into the wild black yonder. One of them aged a little quicker, which in stellar terms means it puffed up and became a red giant, engulfing and merging with its sibling.

The result was what astronomers call a “blue straggler“, a “re-born” young star that comes from a stellar merger.

The astronomers are now working on finding the origin of four other lone stars on the far outskirts of the Milky Way.

Story by Jonathan Nally, Editor, SpaceInfo.com.au

Image credits: illustrations, NASA / ESA / G. Bacon, A. Field and Z. Levay (STScI); science, NASA / ESA / O. Gnedin (University of Michigan, Ann Arbor), and W. Brown (Harvard-Smithsonian Centre for Astrophysics, Cambridge, Mass.)

Get SpaceInfo.com.au daily updates by RSS or email! Click the RSS Feed link at the top right-hand corner of this page, and then save the RSS Feed page to your bookmarks. Or, enter your email address (privacy assured) and we’ll send you daily updates. Or follow us on Twitter, @spaceinfo_oz