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Lone star has two planets

A NEW GIANT PLANET has been located in a star system about 250 light-years from Earth. The planet, perhaps twice the mass of Jupiter, could help researchers learn more about how extrasolar planets are formed.

An extrasolar (‘beyond the Solar System’) planet is one that belongs to a star system other than our own.

The star system harbouring the new planet contains only one star, as do the other three systems with extrasolar planets analysed by San Francisco State University astronomer Stephen Kane, an assistant professor of physics and astronomy, and his colleagues. It is a surprising finding, given the high rate of multiple-star systems in our solar neighbourhood.

“There is a great interest in these stars that are known to host planets,” Kane explained, since astronomers suspect that planet formation in a multi-star system would be very different from planet formation in a single-star system like our own.

False-colour image of star HD 4230

This false-colour image shows the star HD 4230, located about 250 light-years from Earth. Measurements indicate the presence of two, unseen, planets orbiting it.

A multiple-star system “might have not one but two” flattened clouds, called discs, where planets form, he said. “Or it could be that having an extra star would be disruptive, and its gravity could cause any protoplanets to pull apart.”

Relatively few extrasolar planets have been found in multiple-star systems, “but we know that they are there,” Kane said.

A wobbling star

In the four systems studied by the researchers, using optical imaging data collected at the Gemini North observatory in Hawaii, there were some intriguing signs that perhaps a second star – or something else – was present.

In each system, the extrasolar planets were discovered by the radial velocity technique, which measures variations in the speed at which a star moves away and toward Earth, “wobbled” by the gravitational pull of a nearby cosmic body. Depending on the radial velocity signature, astronomers can calculate whether the wobble is coming from a planet or star.

In the star systems studied by Kane and his colleagues, there was a part of the radial velocity data that couldn’t be explained entirely by the pull of an orbiting planet. And at the same time, the planets that had already been discovered in these systems followed eccentric orbits, swinging away from their stars in a less circular and more elliptical fashion, “more like that of a comet,” Kane said.

An unexplained velocity

With these two clues, the researchers wondered if the radial velocity and eccentric orbits might be explained by the presence of another star in the system. But when they took a closer look at the systems, they were able to rule out the possibility that another star was perturbing the system.

Depiction of planetary orbits around HD 168443

The two solid circles marked b and c, depict the orbits of planets circling HD 168443, one of the stars studied by Stephen Kane and his colleagues. The dashed circles represent the size of the orbits of Mercury, Venus Earth and Mars in our Solar System.

“I thought we were likely to find stellar companions, and when all four didn’t have a binary star, that did surprise me,” Kane said.

But in the case of one star, HD 4230, the unexplained radial velocity appears to be coming from the pull of a previously undiscovered giant planet, the researchers report. They confirmed the planet’s presence with additional radial velocity data collected at Hawaii’s Keck observatory.

Given that the researchers did not find any stellar companions, Kane says it is very likely that the leftover radial velocity is instead a signal that there are additional planets to be found in all four systems. The researchers feel this is especially true for the system called HD 168443, where their ability to detect a companion star was very strong.

Adapted from information issued by San Francisco State University.

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Black hole destroys its own ‘dinner’

Artist’s illustration of the outflow in the heart of galaxy Markarian 231

Artist’s illustration of the outflow in the heart of galaxy Markarian 231, produced by a black hole.

A VORACIOUSLY FEEDING black hole creates a ‘wind’ that pushes its own ‘food’ of dust and gas out of reach, astronomers using the Gemini North telescope in Hawai’i have found.

They think this is the process that turned actively feeding black holes—common in the early universe—into the quiescent ones found in galaxies today.

“It looks like they’ve found the ‘off switch’ for black holes,” said Professor Joss Bland-Hawthorn of the University of Sydney, who studies galactic winds.

“We’ve long suspected that a negative feedback process like this must be at work, but these Gemini observations are the first clear evidence of outflows that can starve a black hole of fuel.”

The research will be published in the Astrophysical Journal on 10 March.

Galaxy Markarian 231

The galaxy Markarian 231 contains a massive black hole that is pushing gas and dust away from itself. Hubble Space Telescope image.

Astronomers Professor Sylvain Veilleux (University of Maryland, USA) and Dr David Rupke (Rhodes College, Tennessee, USA) studied the galaxy Markarian 231, which lies 600 million light-years away.

Markarian 231 is a ‘train wreck’ resulting from the collision of two galaxies. At its centre is a black hole at least ten million times the mass of the Sun, which is sucking in gas and dust from its immediate surroundings.

Galactic centre boiling over

The black hole in Markarian 231 was known to produce narrow outflows (‘jets’) but the Gemini observations have revealed a broad outflow extending in all directions for at least 8,000 light-years around the galaxy’s core.

More than one physical process is likely to be creating the outflow. One is thought to be the X-rays and gamma rays generated around the black hole, which heat up the gas in the galaxy’s centre until it ‘boils over’.

Gas is streaming away from the galaxy’s centre at speeds of over 1,000 kilometres a second—fast enough to travel from Sydney to Perth in four seconds. The flow is sweeping away huge amounts of gas.

“The fireworks of new star formation and black hole feeding are coming to an end, most likely as a result of this outflow,” Rupke said.

As extreme as Markarian 231 appears, Veilleux says that it is probably not unique. In the early universe galaxies like this “are seen in large numbers and all of them may have gone through shedding events like the one we are witnessing in Markarian 231,” he said.

Australia has a 6.2% share of the international Gemini partnership. Australian astronomers’ access to the Gemini telescopes is managed through the Australian Gemini Office, hosted by the Australian Astronomical Observatory (AAO), Australia’s national optical observatory. The AAO is part of the Commonwealth Department of Innovation, Industry, Science and Research.

Adapted from information issued by AAO. Markarian 231 courtesy NASA / ESA / Hubble Heritage Team / A. Evans. Illustration courtesy Gemini Observatory / AURA / Lynette Cook. Gemini telescope image courtesy Gemini Observatory.

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“Failed star” orbits Sun look-alike

PZ Tel A and PZ Tel B

The Sun-like star, PZ Tel A and its brown dwarf companion, PZ Tel B. The majority of light from PZ Tel A has been blocked using specialised image analysis techniques. For distance comparison, the size of Neptune's orbit is shown.

  • Brown dwarf, a “failed star”, spotted
  • 36 times the mass of Jupiter
  • Orbits a younger version of our Sun

Astronomers have made a direct image of brown dwarf in a close orbit around a young, Sun-like star. Brown dwarfs are a class of astronomical bodies that are bigger than planets but smaller than genuine stars. They’re often called “failed stars”.

The team was led by Beth Biller and Michael Liu from the University of Hawaii (UA). They used the huge 8-metre Gemini South telescope in Chile, which is operated by a consortium of countries, including Australia.

Dubbed PZ Tel B, the brown dwarf was spotted at a distance of only 18 astronomical units (AU) from its parent star, known as PZ Tel A.

An astronomical unit is a standard measurement used by astronomers, being the average distance between the Sun and the Earth. At 18 AU, PZ Tel B is at the equivalent of the orbit of Uranus in our Solar System.

The brown dwarf is not visible in an image made back in 2003, suggesting it was at that time closer to and lost in the glare of its parent star.

“Because PZ Tel A is a rare star being both close and very young, it had been imaged several times in the past” said Laird Close, a professor at UA’s Steward Observatory. “So we were quite surprised to see a new companion around what was thought to be a single star.”

The new observations confirm that the brown dwarf is currently moving outward from the main star. They also show that it is 36 times the mass of Jupiter, the largest planet in our Solar System.

“PZ Tel B travels on a particularly eccentric orbit—in the last 10 years, we have literally watched it careen through its inner solar system,” said Beth Biller, lead author of the scientific paper. “This can best be explained by a highly eccentric, or oval-shaped, orbit.”

Brown dwarf size compared to Jupiter, the Sun and the Earth

The size of a brown dwarf compared to Jupiter, the Sun and the Earth (to scale). Brown dwarfs are more massive than planets and less massive than stars, but have similar diameters to planets such as Jupiter.

A young version of our Sun

The host star, PZ Tel A, is similar to our Sun, but at 12 million years of age is about 400 times younger. Astronomers are keen to study it and other such stars to learn more about the formation and evolution of Sun-like stars.

PZ Tel A is expected to retain a surrounding cloud of gas and dust from which planets might form. The gravitational pull of the brown dwarf could upset the formation of any such planets.

The find was made using the Near-Infrared Coronagraphic Imager (NICI) instrument, which blocks out much of the glare of a star and enables nearby regions to be seen.

The brown dwarf is so close to its parent star that it required all the power of NICI, plus adaptive optics—which help to remove the blurring effect of the Earth’s atmosphere—plus special image enhancing techniques, to pick it out of the glare.

NICI is so powerful that it can detect objects 1 million times fainter than their host stars at very close distances.

An international team is using NICI to conduct a 300-star survey, and it will be fascinating to see what they find.

“We are just beginning to glean the many configurations of solar systems around stars like the Sun,” said NICI Campaign leader Michael Liu. “The unique capabilities of NICI provide us with a powerful tool for studying their constituents using direct imaging.”

Also involved in the PZ Tel B research were graduate students Eric Nielsen, Jared Males and Andy Skemer.

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

Images by Jon Lomberg / Gemini Observatory / Beth Biller / Gemini NICI Planet-Finding Campaign.

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Confirmed: first image of distant planet

Star 1RXS J160929.1-210524 and its planet

This image, first released in September of 2008, shows the star 1RXS J160929.1-210524 and its ~8 Jupiter-mass companion (within red circle), which has now been confirmed as a planet.

  • Planet first spotted in 2008; needed confirmation
  • Now known to orbit a star 500 light-years from Earth
  • A scorching 1,500ºC; still cooling down

A planet only about 8 times the mass of Jupiter has been confirmed orbiting a Sun-like star at over 300 times farther from the star than the Earth is from our Sun.

It is the least-massive planet known to orbit at such a great distance from a star.

The discovery utilised high-resolution adaptive optics technology at the Gemini Observatory to take direct images and light spectra of the planet.

First reported in September 2008 by a team led by David Lafrenière (then at the University of Toronto, now at the University of Montreal and Centre for Research in Astrophysics of Quebec), the suspected planetary system required further observations over time to confirm that the planet and star were indeed moving together through space.

Back in 2008, all astronomers knew for sure was that the young, planetary mass object appeared to be sitting right next to the young Sun-like star.

The closeness of the two objects strongly suggested that they were linked, but it was still possible (though unlikely) that they were unrelated and only aligned by chance.

According to Lafrenière, “Our new observations rule out this chance alignment possibility, and thus confirms that the planet and the star are related to each other.”

With this confirmation the system, known as 1RXS J160929.1-210524 (or 1RXS 1609 for short), provides scientists with a unique specimen that challenges planetary formation theories because of its extreme distance from the star.

“The unlikely locale of this alien world could be telling us that nature has more than one way of making planets,” says co-author Ray Jayawardhana of the University of Toronto.

An infrared image of the 1RXS 1609 system

An infrared (heat) image of the system, revealing the planet to be a scorching 1,500 degrees Celsius.

“Or, it could be hinting at a violent youth when close encounters between newborn planets hurl some siblings out to the hinterlands,” he adds.

First to be directly imaged

With its initial detection by the team using the Gemini Observatory in April of 2008, the object became the first likely planet known to orbit a Sun-like star to be revealed by direct imaging (rather than the indirect through which most such planets have been found).

At the time of its discovery the team also obtained a spectrum of the light from the planet and was able to determine many of its characteristics, which are confirmed in this new work.

Since the initial observations several other worlds have been discovered using direct imaging, including a system of three planets around the star HR 8799 also discovered with Gemini. However, the planets around HR 8799 orbit much closer to their host star.

The team’s recent work on 1RXS 1609 also verified that no additional large planets (between 1-8 Jupiter masses) are present in the system closer to the star.

Future observations should make it possible to measure a very precise velocity of the planet relative to its host star. This will show whether the planet is on a roughly circular orbit, as would be expected if it really formed far from its host star; or whether it is in a very non-circular or even “open” orbit, as could be the case if it formed closer to its star, but was gravitationally “kicked out” following a close encounter with another planet.

Scorching hot planet

The host star is located about 500 light-years away in a group of young stars called the Upper Scorpius association that formed about five million years ago. The original survey studied more than 85 stars in this association.

The planet has an estimated temperature of about 1,500 degrees Celsius and is much hotter than Jupiter, which has a atmospheric cloud-top temperature of about 160 Kelvin (-110 degrees Celsius). The host star has an estimated mass of about 85% that of our Sun.

The Gemini North observatory in Hawai'i

The Gemini North observatory in Hawai'i

The young age of the system explains the high temperature of the planet. The contraction of the planet under its own gravity during its formation quickly raised its temperature to thousands of degrees. With this contraction phase over, the planet is slowly cooling down by radiating infrared light (heat). In billions of years, the planet will eventually reach a temperature similar to that of Jupiter.

High-tech telescope

The observations used the Near-Infrared Imager (NIRI) and the Altair adaptive optics system on the Gemini North telescope. Adaptive optics allows scientists to remove much of the distortions caused by our atmosphere and dramatically sharpen views of space.

“Without adaptive optics, we would simply have been unable to see this planet,” says Lafrenière. “The atmosphere blurs the image of a star so much that it extends over and is much brighter than the image of a faint planet around it, rendering the planet undetectable.”

“Adaptive optics removes this blurring and provides a better view of faint objects very close to stars.”

The Gemini Observatory is an international collaboration with two identical 8-metre telescopes. The Frederick C. Gillett Gemini Telescope is located at Mauna Kea, Hawai’i (Gemini North) and the other telescope at Cerro Pachón in northern Chile (Gemini South).

Together, they provide full coverage of both hemispheres of the sky. Both telescopes incorporate new technologies that allow large, relatively thin mirrors under active control to collect and focus both optical and infrared radiation from space.

Countries in the Gemini partnership are the USA, UK, Canada, Chile, Argentina, Australia and Brazil.

Adapted from information issued by Gemini Observatory / AURA / David Lafrenière (University of Montreal) / Ray Jayawardhana (University of Toronto) / Marten van Kerkwijk (University of Toronto).

Monster galaxy turns cannibal

Supermassive galaxy (ESO 146-IG 005) is clearly visible in the centre of a galaxy group

A supermassive galaxy (ESO 146-IG 005) is clearly visible in the centre of a galaxy group, along with the remains of at least four other galaxies that are being “digested” by it. ESO 146-IG 005 is thought to be the most massive galaxy in our local universe.

  • 30 trillion times the Sun’s mass
  • Biggest galaxy in our neighbourhood
  • Cosmic cannibal, eating other galaxies

A newly discovered “gravitational lens” in a relatively nearby galaxy cluster is leading astronomers to conclude that the cluster hosts the most massive galaxy known in our local universe.

The study also reaffirms that galactic cannibalism is one reason that this galaxy is so obese, tipping the scales at up to 30 trillion times the mass of our Sun.

The supermassive galaxy is located at the core of the galaxy cluster Abell 3827, which lies some 1.4 billion light-years away. This galaxy and hundreds of its smaller cluster companions are visible in a dramatic new image released by the Gemini Observatory.

The image is part of an upcoming scientific paper that reports on the study of the massive galaxy using the gravitational lens formed by its core (also visible in the image) to provide new measurements of the galaxy’s extreme mass.

Although this bright galaxy (known as ESO 146-IG 005) dominates the core of Abell 3827, “the magnitude of its appetite has not been fully appreciated,” said Gemini astronomer Rodrigo Carrasco, who is a member of the team that used the 8-metre Gemini South telescope in Chile to study this galaxy and its cluster. The Gemini observations revealed, for the first time, the effects of gravitational lensing near the core of ESO 146-IG 005.

Distant galaxies distorted by the gravity of a foreground galaxy

The giant galaxy's gravity acts like a lens to distort the shape of galaxies that lie way beyond, making them look like streaks and arcs.

A gravitational lens is created when a massive object (in this case the core of the supermassive galaxy) distorts its local space. Light from a more distant background galaxy (in this case two galaxies) that is passing by appears deflected from its original path.

From our perspective, we see the background galaxies’ light reshaped as a ring-like structure and arcs around the lensing object. These arcs from both galaxies are clearly visible in the new Gemini images.

“The gravitational lens we discovered allowed us to estimate for the first time the mass of this monster galaxy very accurately. The inferred mass is a factor of 10 greater than previous estimates derived from X-ray observations,” said Carrasco. “Assuming our model is correct, this is by far the most massive galaxy known in our local universe.”

This galaxy’s a messy eater

The exceptional galaxy was not simply born massive; it has grown by consuming its companions in perhaps the most extreme example of ongoing “galaxy cannibalism” known.

“This unabashed cannibal is something of a messy eater, with the partially digested remains of at least four smaller galaxies still visible near its centre,” said team member Michael West, astronomer at the European Southern Observatory.

“Eventually this galaxy will grow even bigger judging by the number of nearby galaxies already within its gravitational grasp.”

These observations yield important insight into the process of galaxy growth, especially of elliptical-shaped galaxies; these galaxies do not appear to have acquired their full mass quickly in the early universe, but instead show significant growth through mergers and cannibalism at later times, after many of their stars have formed. The resulting galaxies, such as this one, can be extremely massive.

The Gemini observations were made using the Gemini Multi-Object Spectrograph (GMOS) on the Gemini South telescope in Chile. Follow-up spectroscopic observations used the same instrument to confirm the distances of the two background galaxies whose light is diverted by the gravitational potential of the cluster core. These two galaxies were found to lie at about 2.7 and 5.1 billion light-years away.

The enclosure of the Gemini South observatory in Chile.

The Gemini South observatory in Chile.

The international Gemini Observatory

The Gemini Observatory is an international collaboration with two identical 8-metre telescopes. The Frederick C. Gillett Gemini Telescope is located at Mauna Kea, Hawai’i (Gemini North), and the other telescope at Cerro Pachon in northern Chile (Gemini South), and hence provide full coverage of both hemispheres of the sky. Both telescopes incorporate new technologies that allow large, relatively thin mirrors under active control to collect and focus both optical and infrared radiation from space.

The Gemini Observatory provides the astronomical communities in each partner country with state-of-the-art astronomical facilities that allocate observing time in proportion to each country’s contribution. In addition to financial support, each country also contributes significant scientific and technical resources.

The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the UK Science and Technology Facilities Council (STFC), the Canadian National Research Council (NRC), the Chilean Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT), the Australian Research Council (ARC), the Argentinean Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), and the Brazilian Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq).

Adapted from information issued by Gemini Observatory / Gemini Legacy Image: R. Carrasco et al., Gemini Observatory/AURA.