Space and Astronomy news daily - SpaceInfo.com.au » Astronomy

Tiny galaxy with a bright nebula

Jonathan Nally — Wed, 16 May 2012 13:01:32 +0000

The dwarf galaxy NGC 2366 might be small and dim, but it is home to a surprisingly bright, star-forming nebula—the blue patch in the top-right corner—and close enough so that its individual stars can be made out.

THE STARRY SMOG stretching across this image obtained by the Hubble Space Telescope is the central part of the dwarf galaxy known as NGC 2366. The most obvious feature in this galaxy is a large nebula visible in the upper-right part of the image, an object known as NGC 2363.

A nearby yellowish swirl is not in fact part of the nebula. It is a spiral galaxy much further away, whose light is shining right through NGC 2366. This is possible because galaxies are not solid objects. Galaxies are overwhelmingly made up of the empty space between stars.

NGC 2366 and NGC 2363 are located about 10 million light-years away. As a dwarf galaxy, NGC 2366’s size is in the same ballpark as the two main satellite galaxies of our Milky Way, named the Large and Small Magellanic Clouds. Like the Magellanic Clouds, NGC 2366′s lack of well-defined structure leads astronomers to further classify it as an irregular galaxy.

Although NGC 2366 might be small by the standards of galaxies, many of its stars are not, and the galaxy is home to numerous gigantic blue stars. The blue dots scattered throughout the galaxy speak to the burst of star formation that the galaxy has undergone in recent cosmic time. A new generation of these stellar titans has lit up the nebula NGC 2363.

In gas-rich star-forming regions, the ultraviolet radiation from young, big, blue stars excites the hydrogen gas, making it glow. NGC 2363, as well as other, smaller patches seen throughout Hubble’s image, are the latest birth sites for stellar giants.

Imaged through green and infrared filters, these nebulae take on a blue-ish tinge in this image, though their actual colour is a shade of red.

Adapted from information issued by NASA / ESA.

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Sparkling sphere of ancient stars

Jonathan Nally — Mon, 14 May 2012 14:00:55 +0000

Messier 55 is a huge ball of very old stars, about 17,000 light-years from Earth.

A NEW IMAGE of Messier 55 from the European Southern Observatory’s (ESO) VISTA infrared survey telescope shows tens of thousands of stars crowded together like a swarm of bees. Besides being packed into a relatively small space, these stars are also among the oldest in the Universe. Astronomers study Messier 55 and other ancient objects like it, called globular star clusters, to learn how galaxies evolve and stars age.

Globular clusters are held together in a tight spherical shape by gravity. In Messier 55, the stars certainly do keep close company—approximately one hundred thousand stars are packed within a sphere with a diameter of only about 25 times the distance between the Sun and the nearest star system, Alpha Centauri.

About 160 globular clusters have been spotted encircling our galaxy, the Milky Way, mostly toward its bulging centre. The largest galaxies can have thousands of these rich collections of stars in orbit around them.

A wider view of Messier 55 at visible light wavelengths. It's easy to see how these vast collections of stars got their name…"globular star clusters". Courtesy ESO and Digitised Sky Survey 2.

Observations of globular clusters’ stars reveal that they originated around the same time—more than 10 billion years ago—and from the same cloud of gas. As this formative period was just a few billion years after the Big Bang, nearly all of the gas on hand was the simplest, lightest and most common in the cosmos—hydrogen, along with some helium and much smaller amounts of heavier chemical elements such as oxygen and nitrogen.

Being made mostly from hydrogen distinguishes globular cluster residents from stars born in later eras, like our Sun, that are infused with heavier elements formed in earlier generations of stars. The Sun lit up some 4.6 billion years ago, making it only about half as old as the elderly stars in most globular clusters.

The new image was obtained in infrared light by the 4.1-metre Visible and Infrared Survey Telescope for Astronomy (VISTA) at ESO’s Paranal Observatory in northern Chile.

As well as the stars of Messier 55, this VISTA image also records many galaxies lying far beyond the cluster. A particularly prominent edge-on spiral galaxy appears like a thin, red smudge to the upper right of the centre of the picture.

Adapted from information issued by ESO / J. Emerson / VISTA. Acknowledgment: Cambridge Astronomical Survey Unit.

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Rogue stars sail in intergalactic space

Jonathan Nally — Sun, 13 May 2012 14:00:41 +0000

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, 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.

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Do free-floating planets outnumber stars?

Jonathan Nally — Sat, 12 May 2012 09:44:27 +0000

Could there be untold billions of planets wandering free through space?

A FEW HUNDRED THOUSAND BILLION free-floating, life-bearing, Earth-size planets may exist in the space between stars in the Milky Way. So argues an international team of scientists led by Professor Chandra Wickramasinghe, Director of the Buckingham Centre for Astrobiology at the University of Buckingham, UK.

The scientists have proposed that these life-bearing planets originated in the early universe within a few million years of the Big Bang, and that they make up most of the so-called “missing mass” within galaxies.

The scientists have calculated that such a planetary body would cross through the inner Solar System every 25 million years on the average. They say that during each transit, interplanetary dust—including a component of the Solar System’s living cells—would become implanted at its surface.

The free-floating planet would then have the added property of mixing the products of local biological evolution on a galaxy-wide scale.

The team’s findings have been published online in the journal Astrophysics and Space Science.

Adapted from information issued by Springer. Image courtesy ESO.

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Giant asteroid’s secrets revealed

Jonathan Nally — Thu, 10 May 2012 20:57:15 +0000

NASA's Dawn mission has begun to reveal Vesta's complex history. The 110-kilometre-wide dwarf planet is the second-largest body in the asteroid belt.

NASA’s DAWN SPACECRAFT has provided researchers with the first close-up analysis of the giant asteroid Vesta, yielding new insights into its creation and kinship with terrestrial planets and Earth’s Moon.

Vesta now has been revealed as a special fossil of the early Solar System with a more varied, diverse surface than originally thought. Scientists have confirmed a variety of ways in which Vesta more closely resembles a small planet or Earth’s Moon than another asteroid.

“Dawn’s visit to Vesta has confirmed our broad theories of this giant asteroid’s history, while helping to fill in details it would have been impossible to know from afar,” said Carol Raymond, deputy principal investigator at NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

“Dawn’s residence at Vesta of nearly a year has made the asteroid’s planet-like qualities obvious and shown us our connection to that bright orb in our night sky.”

Complex history

Scientists now see Vesta as a layered, planetary building block with an iron core—the only one known to survive the earliest days of the Solar System.

The asteroid’s geologic complexity can be attributed to a process that separated the asteroid into a crust, mantle and iron core with a radius of approximately 110 kilometres about 4.56 billion years ago. The terrestrial planets and Earth’s Moon formed in a similar way.

Family history: Mars, Mercury, Earth's Moon and the dwarf planet Ceres.

Dawn observed a pattern of minerals exposed by deep gashes formed by space rock impacts, which may support the idea the asteroid once had a subsurface magma ocean.

A magma ocean occurs when a body undergoes almost complete melting, leading to layered building blocks that can form planets. Other bodies with magma oceans ended up becoming parts of Earth and other planets.

Meteorite matches

Data also confirm that a distinct group of meteorites found on Earth did, as theorised, originate from Vesta. The signatures of pyroxene—an iron- and magnesium-rich mineral—in those meteorites match those of rocks on Vesta’s surface.

These objects account for about 6 percent of all meteorites seen falling on Earth.

Chunks of Vesta have fallen on Earth as meteorites. These are slices of some of them.

This makes the asteroid one of the largest single sources for Earth’s meteorites. The finding also marks the first time a spacecraft has been able to visit the source of samples after they were identified on Earth.

Similarity to moons

Scientists now know Vesta’s topography is quite steep and varied. Some craters on Vesta formed on very steep slopes and have nearly vertical sides, with landslides occurring more frequently than expected.

Another unexpected finding was that the asteroid’s central peak in the Rheasilvia basin in the southern hemisphere is much higher and wider, relative to its crater size, than the central peaks of craters on bodies like our Moon.

Vesta also bears similarities to other low-gravity worlds like Saturn’s small icy moons, and its surface has light and dark markings that don’t match the predictable patterns on Earth’s Moon.

“We know a lot about the Moon and we’re only coming up to speed now on Vesta,” said Vishnu Reddy, a framing camera team member at the Max Planck Institute for Solar System Research in Germany and the University of North Dakota in Grand Forks.

Vesta was clobbered by impacts that left huge scars. The largest is called Rheasilvia.

“Comparing the two gives us two storylines for how these fraternal twins evolved in the early Solar System.”

A battered world

Dawn has revealed details of ongoing collisions that battered Vesta throughout its history. Scientists now can date the two giant impacts that pounded Vesta’s southern hemisphere and created the basin Veneneia approximately 2 billion years ago and the Rheasilvia basin about 1 billion years ago. Rheasilvia is the largest impact basin on Vesta.

“The large impact basins on the Moon are all quite old,” said David O’Brien, a Dawn participating scientist from the Planetary Science Institute in Tucson, Arizona. “The fact that the largest impact on Vesta is so young was surprising.”

Launched in 2007, Dawn began exploring Vesta in mid-2011. The spacecraft will depart Vesta on August 26 for its next study target, the dwarf planet Ceres, in 2015.

More information:

NASA’s Dawn mission page

JPL’s Dawn mission page

Adapted from information issued by NASA / JPL-Caltech. Images courtesy NASA / JPL-Caltech / UCLA / University of Tennessee / MPS / DLR / IDA / PSI.

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Light of an alien “super-Earth”

Jonathan Nally — Tue, 08 May 2012 21:25:41 +0000

Artist's concept of the planet 55 Cancri e, a world that orbits its star so closely—about 25 times closer than Mercury is to our Sun—that it is tidally locked with one face forever blistering under the heat of its star.

NASA’S SPITZER SPACE TELESCOPE has detected light emanating from a “super-Earth” planet beyond our Solar System for the first time. While the planet is not habitable, the detection is a historic step toward the eventual search for signs of life on other planets.

While no current telescope is able to show us an image of the planet, Spitzer can detect the spectrum of light coming from it.

The planet, called 55 Cancri e, falls into a class of planets termed super Earths, which are more massive than our home world but lighter than giant planets like Neptune. Fifty-five Cancri e is about twice as big and eight times as massive as Earth. The planet orbits a bright star, called 55 Cancri, in a mere 18 hours.

Previously, Spitzer and other telescopes were able to study the planet by analysing how the light from 55 Cancri changed as the planet passed in front of the star. In the new study, Spitzer measured how much infrared light comes from the planet itself.

The results reveal the planet is likely dark and its sun-facing side is more than 1,700 degrees Celsius, hot enough to melt metal.

Distant water world

The new information is consistent with a prior theory that 55 Cancri e is a water world: a rocky core surrounded by a layer of water in a “supercritical” state where it is both liquid and gas, and topped by a blanket of steam.

“It could be very similar to Neptune, if you pulled Neptune in toward our Sun and watched its atmosphere boil away,” said Michael Gillon of Universite de Liege in Belgium, principal investigator of the research, which appears in the Astrophysical Journal. The lead author is Brice-Olivier Demory of the Massachusetts Institute of Technology in Cambridge.

Artist's impression of the Spitzer Space Telescope

The 55 Cancri system is relatively close to Earth at 41 light-years away. It has five known planets, with 55 Cancri e being the closest to the star and tidally locked, so one side always faces the star. Spitzer discovered the star-facing side is extremely hot, indicating the planet probably does not have a substantial atmosphere to carry the sun’s heat to the unlit side.

Direct measurements

In 2005, Spitzer became the first telescope to detect light from a planet beyond our Solar System. To the surprise of many, the observatory saw the infrared light of a “hot Jupiter,” a gaseous planet much larger than the solid 55 Cancri e.

Since then, other telescopes, including NASA’s Hubble and Kepler space telescopes, have performed similar feats with gas giants using the same method.

In this method, a telescope gazes at a star as a planet circles behind it. When the planet disappears from view, the light from the star system dips ever so slightly, but enough that astronomers can determine how much light came from the planet itself. This information reveals the temperature of a planet, and, in some cases, its atmospheric components. Most other current planet-hunting methods obtain indirect measurements of a planet by observing its effects on the star.

During Spitzer’s ongoing extended mission, steps were taken to enhance its unique ability to see exoplanets, including 55 Cancri e. Those steps, which included changing the cycling of a heater and using an instrument in a new way, led to improvements in how precisely the telescope points at targets.

NASA’s James Webb Space Telescope, scheduled to launch in 2018, likely will be able to learn even more about the planet’s composition. The telescope might be able to use a similar infrared method as Spitzer to search other potentially habitable planets for signs of molecules possibly related to life.

Adapted from information issued by NASA / JPL-Caltech.

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The year ahead in space

Jonathan Nally — Sun, 06 May 2012 18:00:43 +0000

Artist's impression of the Curiosity rover on Mars. The craft is due to arrive on Mars on August 6, 2012.

THIS YEAR IS GOING TO BE A BIG ONE in terms of space activity, and will include some events you’ll be able to experience firsthand. Let’s count down the top five.

At number five we have NASA’s Mars Science Laboratory mission, carrying the Curiosity rover to the Red Planet. Scheduled to arrive on August 6, it will land in Gale Crater (named after a 19th-20th century Australian astronomer, Walter Frederick Gale) and look for signs of organic chemicals. The 900-kilogram, nuclear-powered rover has a primary mission of two years but is expected to last for much longer than that.

At number four we have the total eclipse of the Sun on November 14. The path of totality runs along a narrow west-east strip of far northern Queensland, taking in Cairns and surrounding areas. The thousands of people who are expected to flock to the area will experience two minutes of totality shortly after sunrise—observers elsewhere in Australia will witness a partial eclipse.

After this, the next total solar eclipse to be visible from Australia will be in 2028, when the path of totality will run straight through Sydney.

The transit of Venus will be seen on the morning of June 6 in Australia. There won't be another one until the year 2117.

Coming in at number three is an event you won’t want to miss, as you’ll never get a chance to see another one. It’s the transit of Venus, which will happen on the morning of June 6. A transit occurs when one of the inner planets, in this case Venus, moves between Earth and the Sun and we see it as a small black dot slowly crawling across the solar face. It was to observe a transit of Venus that Captain Cook travelled to the South Pacific in the 18th century … and on his way home bumped into a certain large, dry continent, girt by sea.

Transits of Venus are very rare. They happen in pairs eight years apart (so the last one was in 2004), but between pairs there is a gap of over 100 years. So the 20th century totally missed out, and after June there won’t be another one until the year 2117. So don’t miss it!

Number two on our list is the decision on where the Square Kilometre Array, or SKA, will be built. The SKA will be an enormous network of radio dishes and antennae spread over an area the size of a continent. It will enable astronomers to look back towards the beginning of time, and study the evolution of stars and galaxies throughout cosmic history.

Artist's impression of part of the Square Kilometre Array.

In a situation reminiscent of the Olympics, two regions have put in bids to host the facility and are eagerly awaiting the decision of the international panel. A joint bid by Australia and New Zealand is up against a consortium of southern African countries. The decision could be announced next month. If Australasia gets it, the core of the network will be located in a remote region of Western Australia, but with many other dishes spread out across the nation and into New Zealand.

And so after all of these fantastic events, what could we possibly have in the number one spot on our countdown? What will be this year’s biggest cosmic event? Why, the very survival of Planet Earth of course! In case you haven’t heard, a lot of people seem to be very worried about two things—the apparent end of the Mayan Long Count calendar in December (and the implied end of civilisation as we know it), and a collision between Earth and a planet called Nibiru.

Well, as far as the Mayan calendar is concerned, there is no cause for alarm. Like the Gregorian calendar we use every day, it will simply tick over to a new Long Count and we’ll all live happily every after.

That is, unless we get wiped out by that collision with Nibiru. Frightened? Don’t be. For you see, there’s a basic flaw in the Nibiru hypothesis, and it’s simply this … Nibiru doesn’t exist. It’s a fiction invented by some loopy, cosmic conspiracy nutters. There is no evidence for such a planet, and no evidence that Earth is in any danger from a collision with any other planet, known or unknown. Phew!

UPDATE, February 6: BTW, I misspoke on the Today Show this morning, saying that the next total solar eclipse after this year’s one will occur in the year 2128. I should have said 2028 of course.

Story by Jonathan Nally

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Video: Mystery X-ray source in distant galaxy

Jonathan Nally — Sun, 06 May 2012 02:00:55 +0000

SINCE THE 1980s, astronomers have known about a mysterious class of objects that they call “ultraluminous X-ray sources,” or ULXs. They named them this because these objects give off more X-rays than most other binary star systems where black holes or neutron stars are in orbit around a normal companion star.

Recently, scientists using NASA’s Chandra X-ray Observatory and optical telescopes spotted a ULX in the spiral galaxy M83 that was acting even more strangely. This ULX increased its output in X-rays by 3,000 times over the course of several years.

Using clues found in the X-ray and optical data, researchers think this ULX may be a member of a population of black holes that up until now was suspected to exist but had not been confirmed.

These black holes, which are the smaller stellar-mass black holes (ones that form from the collapse of a giant star), are older and more active than previously thought.

Video courtesy NASA / CXC. Image close-ups – X-ray, NASA / CXC / Curtin University / R. Soria et al.; optical, NASA / STScI / Middlebury College / F. Winkler et al.

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Three space missions extended

Jonathan Nally — Sun, 08 Apr 2012 14:00:55 +0000

Artist's concepts of Spitzer, Planck and Kepler. NASA extended Spitzer and Kepler for two additional years; and the US portion of Planck, a European Space Agency mission, for one year. (Relative sizes not to scale.)

NASA HAS EXTENDED three missions—Kepler, the Spitzer Space Telescope and the US portion of the European Space Agency’s Planck mission—as a result of the 2012 Senior Review of Astrophysics Missions.

“This means scientists can continue using the three spacecraft to study everything from the birth of the universe with Planck, and galaxies, stars, planets, comets and asteroids with Spitzer, while Kepler is determining what percentage of Sun-like stars host potentially habitable Earth-like planets,” said Michael Werner, the chief scientist for astronomy and physics at JPL.

Kepler has been approved for extension through fiscal year 2016, providing four additional years to find Earth-size planets in the habitable zone—the region in a planetary system where liquid water could exist on the surface of the orbiting planet—around Sun-like stars in our galaxy.

Spitzer, launched in 2003, will continue to provide the astronomical community with its unique infrared images for another two years. It has continued to explore the cosmos since running out of coolant, as expected, in 2009.

Among its many duties during its “warm mission”, the observatory is probing the atmospheres of planets beyond our Sun and investigating the glow of some of the most distant galaxies known. As requested by the project, Spitzer received two additional years of operations.

NASA will fund an additional year of US participation in the European Space Agency’s Planck mission. Planck, launched in 2009, is gathering data from the very early universe, shortly after its explosive birth in a big bang. Planck’s observations are yielding insight into the origin, evolution and fate of our universe.

More information:

Kepler mission

Spitzer Space Telescope

Planck mission

Adapted from information issued by JPL. Images courtesy NASA / JPL-Caltech.

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Dark matter search narrows

Jonathan Nally — Sun, 08 Apr 2012 03:52:18 +0000

This faint smattering of stars is actually a small galaxy. Scientists have been unable to spot evidence of certain kinds of dark matter particles within this galaxy and nine others.

STUDIES DECADES AGO OF THE ROTATION of galaxies, and of the movement of groups of galaxies, led scientists to conclude that the universe contained more matter than could be detected in the normal ways.

Being unseen at visible wavelengths, and with its nature unknown, the putative matter was dubbed “dark matter“, and according to popular models it comprises over 80 per cent of all the matter in the universe.

In the early years of investigation into this strange phenomenon, two broad candidates emerged—MACHOs and WIMPS.

MACHOs were hypothetical “massive compact halo objects”, ie. large bodies such as dim stars, black holes or large free-floating planets that would inhabit the outer or “halo” regions of a galaxy. WIMPs are hypothetical “weakly interacting massive particles”, ie. sub-atomic particles that could pervade space but not interact much with normal forms of matter.

The research used two-years of data collected by NASA’s Fermi Gamma-ray Space Telescope (artist's impression).

Research programmes failed to find evidence of MACHOs, so dark matter investigations now focus on WIMPs.

WIMPs could take many forms—perhaps as one or more of the familiar particles, such as neutrinos, or maybe as-yet-unknown particles.

In new research using two-years of data from NASA’s Fermi Gamma-ray Space Telescope, a team that includes astrophysicist Jennifer Siegal-Gaskins (Caltech) has been able to rule out certain kinds of WIMPs.

According to some models, when two WIMPs collide, they can annihilate each other and produce a burst of gamma rays with specific wavelengths. Such energy bursts would be detectable with Fermi.

The scientists studied 10 small galaxies that circle our Milky Way galaxy, looking for telltale gamma ray signs of WIMP collisions within them. They didn’t spot any.

This negative result will help scientists by eliminating particular kinds of WIMPs from the field of candidates, and will enable them to focus on searches for other kinds.

More information: New Insights on Dark Matter

Story by Jonathan Nally. Images courtesy NASA / Sonoma State University / Aurore Simonnet / ESO / Digital Sky Survey 2.

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