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Billions of super-Earths “out there”

Jonathan Nally — Wed, 28 Mar 2012 10:00:45 +0000

Artist's impression of a planet circling the star Gliese 581. Astronomers estimate there could be tens of billions of "super-Earth" planets in our galaxy.

ROCKY PLANETS NOT MUCH BIGGER THAN EARTH are very common in the habitable zones around faint red stars, say astronomers.

The habitable zone is the distance from a star where it is neither too hot nor too cold for liquid water to exist on the surface of a rocky planet.

The international team used a “planet finder” instrument to estimate that there are tens of billions of such planets in the Milky Way galaxy alone, and probably about 100 in the Sun’s immediate neighbourhood.

This is the first direct measurement of the frequency of super-Earths around red dwarfs, which account for 80% of the stars in the Milky Way.

This first direct estimate of the number of light planets circling red dwarf stars used observations made with the HARPS spectrograph on the 3.6-metre telescope at the European Southern Observatory’s La Silla Observatory in Chile.

Super-Earths abound

The HARPS team has been searching for exoplanets orbiting the most common kind of star in the Milky Way—red dwarf stars (also known as M dwarfs. These stars are faint and cool compared to the Sun, but very common and long-lived, and therefore account for 80% of all the stars in the Milky Way.

“Our new observations with HARPS mean that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone…,” says Xavier Bonfils (IPAG, Observatoire des Sciences de l’Univers de Grenoble, France), the leader of the team.

Diagram showing the habitable zone (green area) varies depending on the size and temperature of the star. Too close in (red area) and it's too hot; too far out (blue area) and it's too cold.

“Because red dwarfs are so common—there are about 160 billion of them in the Milky Way—this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone.”

The HARPS team surveyed a carefully chosen sample of 102 red dwarf stars in the southern skies over a six-year period. A total of nine super-Earths (planets with masses between one and ten times that of Earth) were found, including two inside the habitable zones of stars Gliese 581 and Gliese 667 C respectively.

The astronomers could estimate how heavy the planets were and how far from their stars they orbited.

By combining all the data, including observations of stars that did not have planets, and looking at the fraction of existing planets that could be discovered, the team has been able to work out how common different sorts of planets are in red dwarf systems.

They find that the frequency of occurrence of super-Earths in the habitable zone is 41% with a range from 28% to 95%.

On the other hand, more massive planets, similar to Jupiter and Saturn in our Solar System, are found to be rare in red dwarf systems. Less than 12% of red dwarfs are expected to have giant planets (with masses between 100 and 1,000 times that of the Earth).

In the zone

As there are many red dwarf stars close to the Sun the new estimate means that there are probably about 100 super-Earth planets in the habitable zones around stars in the neighbourhood of the Sun at distances less than about 30 light-years.

“The habitable zone around a red dwarf, where the temperature is suitable for liquid water to exist on the surface, is much closer to [a red dwarf] star than the Earth is to the Sun,” says Stéphane Udry (Geneva Observatory and member of the team).

“But red dwarfs are known to be subject to stellar eruptions or flares, which may bathe the planet in X-rays or ultraviolet radiation, and which may make life there less likely.”

One of the planets discovered in the HARPS survey of red dwarfs is Gliese 667 Cc. This is the second planet in this triple-star system and it seems to be situated close to the centre of the habitable zone.

This artist’s impression shows a sunset seen from the super-Earth Gliese 667 Cc. The brightest star in the sky is the red dwarf Gliese 667 C, which is part of a triple star system. The other two more distant stars, Gliese 667 A and B appear in the sky also to the right. Astronomers have estimated that there are tens of billions of such rocky worlds orbiting faint red dwarf stars in the Milky Way alone.

Although this planet is more than four times heavier than the Earth it is the closest twin to Earth found so far, and almost certainly has the right conditions for the existence of liquid water on its surface.

Gliese 667 Cc is the second super-Earth planet inside the habitable zone of a red dwarf discovered during this HARPS survey, after Gliese 581d was announced in 2007 and confirmed in 2009.

“Now that we know that there are many super-Earths around nearby red dwarfs we need to identify more of them using both HARPS and future instruments,” concludes Xavier Delfosse, another member of the team.

Some of these planets are expected to pass in front of, or transit, their parent star as they orbit, and astronomers can use these transits to learn more about the planets’ atmospheres and look for signs of life.

Adapted from information issued by ESO / L. Calçada.

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Gallery: The Omega Nebula

Jonathan Nally — Tue, 10 Jan 2012 10:03:34 +0000

This image of the Omega Nebula (Messier 17), captured by the European Southern Observatory's Very Large Telescope (VLT), is one of the sharpest of this object ever taken from the ground. It shows the dusty, rosy central parts of the famous star-forming region.

A NEW IMAGE OF THE HEART of the Omega Nebula, captured by the European Southern Observatory’s (ESO) Very Large Telescope (VLT), is one of the sharpest of this object ever taken from the ground.

It shows the dusty, rose-colored central parts of this famous stellar nursery and reveals extraordinary detail in the cosmic landscape of gas clouds, dust and newborn stars.

The colourful gas and dark dust in the Omega Nebula serve as the raw materials for creating the next generation of stars.

In this particular section of the nebula, the newest stars on the scene—dazzlingly bright and shining blue-white—light up the whole ensemble. The nebula’s smoky-looking ribbons of dust stand in silhouette against the glowing gas.

The dominant reddish colours of this portion of the cloud-like expanse, arise from hydrogen gas, glowing under the influence of the intense ultraviolet rays from the hot young stars.

The Omega Nebula goes by many names, depending on who observed it when and what they thought they saw. These other titles include the Swan Nebula, the Horseshoe Nebula and even the Lobster Nebula. The object has also been catalogued as Messier 17 (M17) and NGC 6618.

The nebula is located about 6,500 light-years away and is a popular target for astronomers, as it ranks as one of the youngest and most active stellar nurseries for massive stars in the Milky Way.

A wider view of the Omega Nebula.

Download wallpapers of the Omega Nebula:

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Adapted from information issued by ESO.

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World’s biggest telescope a step closer

Jonathan Nally — Tue, 13 Dec 2011 05:52:34 +0000

Artist's impression of the European Extremely Large Telescope

A TELESCOPE TO DWARF ALL OTHERS is on the road to being fully approved in mid-2012, with much of the funding secured and work commencing on the road that will provide access to the remote site in Chile.

The European Extremely Large Telescope (E-ELT) will be an optical/infrared telescope with a main mirror 39.3 metres wide. Today’s current largest telescopes have mirrors around the 10-metre mark.

The European Southern Observatory’s (ESO) huge, 1.802 billion Euro facilitywill be built at Cerro Armazones in Chile’s high Atacama desert.

Artist's impression of the E-ELT alongside the Sydney Opera House, to give an idea of scale.

The initial work approved this week includes preparations for the road that will link to the site, and commencement of work on one on the most challenging parts of the telescope…the M4 mirror, an “adaptive optics” mirror that will help to remove the blurring effect of Earth’s atmosphere.

“The E-ELT is starting to become reality,” says the ESO Director General, Tim de Zeeuw. “However, with a project of this size it is expected that approval of the extra expenditure will take time … preparatory work must start now in order for the project to be ready for a full start of construction in 2012.”

Final approval for the E-ELT project is expected to be granted next year.

This video from last year explains more about the amazing E-ELT and the site at which it will be built:

Story by Jonathan Nally. Images and video courtesy ESO.

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“Vampire star” devouring its companion

Jonathan Nally — Sat, 10 Dec 2011 13:01:39 +0000

ASTRONOMERS HAVE OBTAINED the best images ever of a star that has lost most of its material to a vampire companion.

By combining the light captured by four telescopes at the European Southern Observatory’s (ESO) Paranal Observatory (Chile), they created a virtual telescope 130 metres across with vision 50 times sharper than the Hubble Space Telescope.

Surprisingly, the new results show that the transfer of gas from one star to the other in this double system is gentler than expected.

The video above shows a “zoom in”, through several different images of different resolution, ending with what looks like two blobs—a blue one and a orangeish one. These are the real images of the two stars, with the red giant being the bigger one. Images taken on different dates show how the stars have moved in their mutual orbit around each other.

The astronomers observed the unusual system SS Leporis in the constellation of Lepus (The Hare), which contains two stars that circle around each other in 260 days.

The stars are very close together…separated by only a little more than the distance between the Sun and the Earth. In terms of size, the larger and cooler of the two stars (a red giant) is big enough to extend out to one quarter of this distance — corresponding roughly to the orbit of Mercury.

Because of this closeness, the hot companion star has already cannibalised about half of the mass of the larger star.

The new observations are sharp enough to show that the giant star is smaller than previously thought, making it much more difficult to explain how it lost matter to its companion.

The astronomers now think that, rather than streaming from one star to the other, the gas must be expelled from the giant star as a stellar wind and then captured by the hotter companion.

Adapted from information issued by ESO / Digitised Sky Survey 2 / Nick Risinger (skysurvey.org) / PIONIER / IPAG; music: John Dyson (from the album Moonwind).

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Fried Egg nebula home to hypergiant

Jonathan Nally — Fri, 30 Sep 2011 14:02:48 +0000

ASTRONOMERS HAVE TAKEN AN IMAGE of a colossal star that belongs to one of the most rare classes of stars in the Universe…the yellow hypergiants.

The new picture is the best ever taken of a star in this class and shows for the first time a huge dusty double shell surrounding the star.

The star and its shells resemble an egg white around a yolky centre, leading the astronomers to nickname the object the Fried Egg Nebula.

The monster star, known to astronomers as IRAS 17163-3907, has a diameter about a thousand times bigger than our Sun.

And at a distance of about 13,000 light-years from Earth, it is the closest yellow hypergiant found to date and new observations show it shines some 500,000 times more brightly than the Sun.

Unexpected discovery

Yellow hypergiants are in an extremely active phase of their evolution, undergoing a series of explosive events. This particular star has ejected four times the mass of the Sun in just a few hundred years.

The material flung out during these bursts has formed the extensive double shell of the nebula, which is made of dust rich in silicates and mixed with gas.

This picture of the nebula around a rare yellow hypergiant star called IRAS 17163-3907 is the best ever taken of a star in this class and shows for the first time a huge dusty double shell surrounding the star. The star and its shells resemble an egg white around a yolky centre, leading astronomers to nickname the object the Fried Egg Nebula.

“This object was known to glow brightly in the infrared but, surprisingly, nobody had identified it as a yellow hypergiant before,” said Eric Lagadec (European Southern Observatory, ESO), who led the team that produced the new images using ESO’s Very Large Telescope (VLT).

The next supernova?

If the Fried Egg Nebula were placed in the centre of the Solar System the Earth would lie deep within the star itself and the planet Jupiter would be orbiting just above its surface.

The much larger surrounding nebula would engulf all the planets and dwarf planets and even some of the comets that orbit far beyond the orbit of Neptune.

The outer shell has a radius of 10,000 times the distance from the Earth to the Sun.

The star is likely to soon die an explosive death—it will be one of the next supernova explosions in our galaxy.

Supernovae provide much-needed chemicals to the surrounding interstellar environment and the resulting shock waves can kick start the formation of new stars.

Adapted from information issued by ESO / E. Lagadec.

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Over 50 new planets discovered

Jonathan Nally — Mon, 19 Sep 2011 03:42:21 +0000

ASTRONOMERS HAVE ANNOUNCED a rich haul of more than 50 new exoplanets, including 16 super-Earths, one of which orbits at the edge of the habitable zone of its star. By studying the properties of all the planets found so far by this project, the team has found that about 40% of stars similar to the Sun have at least one planet lighter than Saturn.

The discoveries were made using the HARPS spectrograph on the 3.6-metre telescope at the European Southern Observatory’s (ESO) La Silla Observatory in Chile.

The new exoplanets orbit nearby stars, and include sixteen super-Earths. This is the largest number of such planets ever announced at one time.

Planets with a mass between one and ten times that of the Earth are called super-Earths. There are no such planets in our Solar System, but they appear to be very common around other stars. Discoveries of such planets in the habitable zones around their stars are very exciting because—if the planet were rocky and had water, like Earth—they could potentially be an abode of life.

One of the newly discovered planets, HD 85512 b, is estimated to be only 3.6 times the mass of the Earth and is located at the edge of its star’s habitable zone — a narrow zone around a star in which water may be present in liquid form if conditions are right.

Adapted from information issued by ESO / M. Kornmesser.

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Galaxy gazing with The Eyes

Jonathan Nally — Wed, 24 Aug 2011 10:00:30 +0000

A peculiar pair of galaxies, NGC 4438 and NGC 4435, nicknamed The Eyes. The larger of the two, NGC 4438 (top) is thought to have once been a spiral galaxy that was strongly deformed by collisions with other galaxies in the relatively recent past. The two galaxies belong to the Virgo Cluster and are about 50 million light-years away.

The Eyes are two galaxies, NGC 4435 and 4438
Located 50 million light-years from Earth
Probably involved in a collision 100 million years ago

THIS BEAUTIFUL YET PECULIAR pair of galaxies is nicknamed ‘The Eyes’ and is about 50 million light-years from Earth, with the two galaxies some 100,000 light-years apart.

Their nickname comes from the apparent similarity between their cores—two white ovals that resemble a pair of eyes glowing in the dark when seen through a moderate-sized backyard telescope.

But although the centres of these two galaxies look similar, their outskirts could not be more different.

The galaxy in the lower right, known as NGC 4435, is compact and seems to be almost devoid of gas and dust.

In contrast, the large galaxy in the upper left (NGC 4438) has a lane of obscuring dust just below its core, young stars can be seen left of its centre, and gas extends at least up to the edges of the image.

The contents of NGC 4438 have been stripped out by a violent process—a collision with another galaxy that has distorted its spiral shape.

NGC 4435 could be the culprit. Some astronomers think that the damage caused to NGC 4438 resulted from an approach between the two galaxies to within about 16,000 light-years some 100 million years ago.

But while the larger galaxy was damaged, the smaller one was significantly more affected. Gravitational ‘tides’ from the clash are probably responsible for ripping away the contents of NGC 4438, and for removing most of NGC 4435’s gas and dust.

Another possibility is that the giant elliptical galaxy Messier 86, further away from The Eyes and not visible in this image, was responsible for the damage caused to NGC 4438. Recent observations have found filaments of ionised hydrogen gas connecting the two large galaxies, indicating that they may have collided in the past.

Messier 86 and The Eyes belong to the Virgo Cluster, a very rich grouping of galaxies. In such close quarters, galaxy collisions are fairly frequent.

Download wallpapers of The Eyes galaxies (NGC 4438 and NGC 4435):

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Adapted from information issued by ESO / Gems project.

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High and dry – Astronomy in the Atacama

Jonathan Nally — Sat, 13 Aug 2011 14:01:36 +0000

IN THE PURSUIT OF PRISTINE SKIES, ESO—the European Southern Observatory organisation—operates its telescopes far beyond Europe, in the remote and arid landscape of the Atacama Desert in Chile. This ESOcast episode explains why astronomers like to get high and dry.

Adapted from information issued by ESO. Still image courtesy G. Hüdepohl (atacamaphoto.com) / ESO.

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Gallery: A fluffy galaxy

Jonathan Nally — Wed, 10 Aug 2011 11:03:42 +0000

Galaxy NGC 3521 is relatively nearby, at a distance of only 35 million light-years. It's patchy spiral arms give it a fluffy look.

IT’S 35 MILLION LIGHT-YEARS AWAY and 50,000 light-years wide. It’s the spiral galaxy NGC 3521, a spectacular object with a bright and compact core or nucleus, surrounded by richly detailed spiral structure.

This new picture from the European Southern Observatory’s (ESO) Very Large Telescope shows that the most distinctive features of NGC 3521 are its long spiral arms, which are dotted with star-forming regions and interspersed with veins of dust.

The arms are rather irregular and patchy, making NGC 3521 a typical example of a ‘flocculent spiral galaxy’.

These types of galaxies have ‘fluffy’ spiral arms that contrast with the sweeping arms of ‘grand-design spirals’ such as the famous Whirlpool galaxy or M 51, discovered by Charles Messier.

NGC 3521 is bright and relatively close-by, and can easily be seen with a small telescope such as the one used by Messier to catalogue a series of hazy astronomical objects when he was searching for comets in the 1700s.

Strangely, the French astronomer seems to have missed this spiral even though he identified several other galaxies of similar brightness in the constellation of Leo.

It was only in the year that Messier published the final version of his catalogue, 1784, that another famous astronomer, William Herschel, discovered NGC 3521 early on in his more detailed surveys of the northern skies.

Through his larger, 47cm aperture, telescope, Herschel saw a “bright centre surrounded by nebulosity,” according to his observation notes.

In this new VLT picture, colourful, yet ill-defined spiral arms replace Herschel’s “nebulosity”. Older stars dominate the reddish area in the centre while young, hot blue stars permeate the arms further away from the core.

Download wallpapers of the spiral galaxy NGC 3521:

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Adapted from information issued by ESO / O. Maliy.

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Hidden star groups uncovered

Jonathan Nally — Sat, 06 Aug 2011 14:01:43 +0000

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 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).

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