Institute of Astronomy

Astronomy News

'IMPs' on moon point to recent lava flows

12 October 2014 - 6:00pm
Newly found "irregular mare patches" suggest lunar volcanism lasted nearly a billion years longer than thought






Desktop sonic black hole emits Hawking radiation

12 October 2014 - 6:00pm
A model black hole that traps sound instead of light has been caught emitting quantum particles - it could be the first time theoretical Hawking radiation has been seen






Explosive meteors may have seasonal peaks

10 October 2014 - 3:02pm
Powerful incoming meteors like the rock responsible for last year's explosion over Chelyabinsk, Russia, may not be completely random after all






Time-out for blog while catalogue production is underway

10 October 2014 - 11:14am

Credit: ESA/ATG medialab; background: ESO/S. Brunier

We started this blog just over one year ago and what a year it has been! We've had the excitement of  the launch, the fabulous first-light image, the challenges of some aspects of commissioning and, more recently, the relief and satisfaction of getting the 'go' for science, and even the first of Gaia's science alerts.

Now that science data have started to flow, the main activity for scientists working on the mission is preparing for the first catalogue release, planned for summer 2016. So while they are busy with that important task, we will take a break on the blog.

But don't worry, this doesn't mean that there will be no news or updates about the Gaia mission. You will be able to keep in touch with the mission via our websites (Space Science Portal,  Science & Technology, and Cosmos), and you can also follow the progress of Gaia via Twitter (@ESAGaia) and using the Gaia Mission app (for iPhones) which can be downloaded from iTunes.

Thanks to all of you for following us through this exciting first year!

The Gaia Team and Blog Editors

 

Hubble reveals most detailed exoplanet weather map ever [heic1422]

9 October 2014 - 7:00pm
A team of scientists using the NASA/ESA Hubble Space Telescope have made the most detailed map ever of the temperature of an exoplanet's atmosphere, and traced the amount of water it contains. The planet targeted for both of the investigations was the hot-Jupiter exoplanet WASP-43b.

Mapping the weather on WASP-43b

9 October 2014 - 7:00pm

A team of scientists, including astronomers from the University of Cambridge, have made the most detailed map ever of the temperature of an exoplanet’s atmosphere, and traced the amount of water it contains. The planet targeted for both of the investigations was the hot-Jupiter exoplanet WASP-43b, which is about 261 light years away in the Sextans constellation.

WASP-43b is a planet the size of Jupiter, but with double the mass and an orbit much closer to its parent star than any planet in the Solar System. It has one of the shortest years ever measured for an exoplanet of its size — lasting just 19 hours.

A team of astronomers working on two companion studies have now created detailed weather maps of WASP-43b, using data from the NASA/ESA Hubble Space Telescope. One study mapped the temperature at different layers in the planet’s atmosphere, and the other traced the amount and distribution of water vapour within it — detail is shown in the video created by the team.

“Our observations are the first of their kind in terms of providing a two-dimensional map of the planet’s thermal structure,” said Kevin Stevenson from the University of Chicago, lead author of the thermal map study. “These maps can be used to constrain circulation models that predict how heat is transported from an exoplanet's hot day side to its cool night side.”

The planet has different sides for day and night because it is tidally locked, meaning that it keeps one hemisphere facing the star, just as the Moon keeps one face toward Earth. The Hubble observations show that the exoplanet has winds that howl at the speed of sound from a day side that is hot enough to melt iron — soaring above 1500 degrees Celsius — to the pitch-black night side that sees temperatures plunge to a comparatively cool 500 degrees Celsius.

To study the atmosphere of WASP-43b the team combined two previous methods of analysing exoplanets for the first time.

By looking at how the parent star’s light filtered through the planet’s atmosphere — a technique called transmission spectroscopy — they determined the water abundance of the atmosphere on the boundary between the day and night hemispheres.

In order to make the map more detailed the team also measured the water abundances and temperatures at different longitudes. To do this they took advantage of the precision and stability of Hubble’s instruments to subtract more than 99.95% of the light from the parent star, allowing them to study the light coming from the planet itself — a technique called emission spectroscopy. By doing this at different points of the planet’s orbit around the parent star they could map the atmosphere across its longitude.

“We have been able to observe three complete rotations — three years for this distant planet — during a span of just four days,” explained Jacob Bean from the University of Chicago, leader of the research project. “This was essential in allowing us to create the first full temperature map for an exoplanet and to probe its atmosphere to find out which elements it held and where.”
Finding the proportions of the different elements in planetary atmospheres provides vital clues to understanding how planets formed.

“Because there’s no planet with these tortured conditions in the Solar System, characterising the atmosphere of such a bizarre world provides a unique laboratory with which to acquire a better understanding of planet formation and planetary physics,” said Nikku Madhusudhan of Cambridge’s Institute of Astronomy, co-author of both studies. “In this case the discovery fits well with pre-existing models of how such planets behave.”

The team found that WASP-43b reflected very little of its host star’s light. An atmosphere like that on Earth, with clouds that reflect most of the sunlight, is not present on WASP-43b, but the team did find water vapour in the planet’s atmosphere.

“The planet is so hot that all the water in its atmosphere is vapourised, rather than condensed into the icy clouds we find on Jupiter,” said team member Laura Kreidberg of the University of Chicago, lead author of the study mapping water on the planet.

Water is thought to play an important role in the formation of giant planets. Astronomers theorise that comet-like bodies bombard young planets, delivering most of the water and other molecules that we observe. However, the water abundances in the giant planets of the Solar System are poorly known because water is locked away as ice, deep in their atmospheres which makes it difficult to identify.

“Space probes have not been able to penetrate deep enough into Jupiter’s atmosphere to obtain a clear measurement of its water abundance. But this giant planet is different,” added Derek Homeier of the École Normale Supérieure de Lyon, co-author of the studies. “WASP-43b’s water is in the form of a vapour that can be much more easily traced. So we could not only find it, we were able to directly measure how much there is and test for variations along the planet’s longitude.”

In WASP-43b the team found the same amount of water as we would expect for an object with the same chemical composition as the Sun.

“This tells us something fundamental about how the planet formed,” added Kreidberg.“Next, we aim to make water-abundance measurements for different planets to explore their chemical abundances and learn more about how planets of different sizes and types come to form around our own Sun and the stars beyond it.”

The results are presented in two new papers, one on the thermal mapping of the planet’s atmosphere — published online in Science Express on 9 October — and the other on mapping the water content of the atmosphere — published in The Astrophysical Journal Letters on 12 September.

Adapted from European Space Agency press release.

Two new studies have been used to make the most detailed weather map for a planet outside the solar system, where typical daytime highs reach 1500 degrees Celsius and winds exceed the speed of sound.

The atmosphere of such a bizarre world provides a unique laboratory with which to acquire a better understanding of planet formation and planetary physicsNikku MadhusudhanNASA, ESA, and Z. Levay (STScI)Exoplanet WASP-43b orbits its parent star

The text in this work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page. For image rights, please see the credits associated with each individual image.

Yes

Hubble Maps the Temperature and Water Vapor on an Extreme Exoplanet

9 October 2014 - 7:00pm

Get larger image formats

Located 260 light-years away, exoplanet WASP-43b is no place to call home. It is a world of extremes, where seething winds howl at the speed of sound from a 3,000-degree-Fahrenheit day side, hot enough to melt steel, to a pitch-black night side with plunging temperatures below 1,000 degrees Fahrenheit. The Hubble Space Telescope has been used to make the most detailed global map yet of the thermal glow from this turbulent world. The astronomers were also able to map temperatures at different layers of the world's atmosphere and traced the amount and distribution of water vapor. The Jupiter-sized planet lies so close to its orange dwarf host star that it completes an orbit in just 19 hours. The planet is also gravitationally locked so that it keeps one hemisphere facing the star.

NASA's Hubble Maps the Temperature and Water Vapor on an Extreme Exoplanet

9 October 2014 - 5:00pm
A team of scientists using NASA’s Hubble Space Telescope has made the most detailed global map yet of the glow from a turbulent planet outside our solar system, revealing its secrets of air temperatures and water vapor.

Astronomers discover the ‘Mighty Mouse’ of stellar remnants

8 October 2014 - 6:00pm

“You might think of this pulsar as the ‘Mighty Mouse’ of stellar remnants,” said Fiona Harrison of the California Institute of Technology. “It has all the power of a black hole but with much less mass.”

The discovery, made with NASA's Nuclear Spectroscopic Telescope Array (NuSTAR), is helping astronomers better understand mysterious sources of fierce X-rays, called ultraluminous X-ray sources, or ULXs. Before now, all ULXs were thought to be black holes. New data from NuSTAR show that at least one ULX, about 12 million light-years away in the galaxy Messier 82 (M82), is actually a pulsar.

“The pulsar appears to be eating the equivalent of a black hole diet,” said Harrison, NuSTAR principal investigator.

The discovery, reported in the October 9 issue of the journal Nature, will help astronomers understand how black holes gorge, and grow, so quickly – an important event in the formation of galaxies and structures in the universe.

“This is a surprising and fascinating discovery,” said Professor Andy Fabian of Cambridge’s Institute of Astronomy, one of the paper’s co-authors. “The true nature of ULXs has remained hidden since their discovery about 20 years ago and now one of them is shown to be a pulsar which is nearly 100 times brighter than it should be, according to current accretion ideas. We're all wondering how many other ULXs are similar.”

ULXs are generally thought to be black holes feeding, or accreting, off companion stars. They are suspected to be the long-sought medium-size black holes – missing links between smaller, stellar-size black holes and the gargantuan ones that dominate the hearts of all galaxies. But research into the true nature of ULXs is ongoing.

NuSTAR didn't initially set out to study the two ULXs in M82. Astronomers had been observing a recent supernova in M82, when they noticed a pulse of bright X-rays coming from a point nearby – what turned out to be the ULX called M82 X-2. Black holes don't pulse, but pulsars do.

Pulsars belong to a class of stars called neutron stars. Like black holes, neutron stars are the burnt-out cores of exploded stars, only puny in mass by comparison. Pulsars, discovered by Cambridge’s Jocelyn Bell and Antony Hewish in 1967, are neutron stars that send out beams of light. As the star spins, these beams intercept Earth like lighthouse beacons, producing a pulsed signal.

“We took it for granted that the powerful ULXs must be massive black holes,” said Matteo Bachetti, lead author of the paper from the University of Toulouse. “When we first saw the pulsations in the data, we thought they must be from another source.”

NASA's Chandra X-ray Observatory and Swift satellite had also been monitoring M82 to study the same supernova, and confirm that the intense X-rays of M82 X-2 were coming from a pulsar.

“Having a diverse array of telescopes in space means that they can help each other out,” said Paul Hertz, director of NASA's astrophysics division in Washington. “When one telescope makes a discovery, others can be called in for backup.”

The key to NuSTAR's discovery was in its sensitivity to X-rays in the highest-energy ranges as well as its ability to precisely measure the timing of the signals. This timing capability allowed the astronomers to measure a pulse rate from M82 X-2 of 1.37 seconds. They also measured its energy output at the equivalent of 10 million suns, or 10 times more than what was measured before – a big punch for something about the mass of the sun and half the size of Cambridge.

How is this puny dead star radiating so fervently? Astronomers aren't sure, but they say it is likely due to a lavish feast of the cosmic kind. As is the case with black holes, the gravity of a neutron star can pull matter off companion stars. As the matter is dragged into the neutron star, it heats up and glows with X-rays. If the pulsar is indeed feeding off surrounding matter, it is doing so at such an extreme rate to have theorists scratching their heads.

Astronomers are planning follow-up observations with NuSTAR, Swift and Chandra to help explain the bizarre behavior. The NuSTAR team will also look at more ULXs, and it's possible they could turn up more pulsars. At this point, it is not clear if the M82 X-2 is an oddball or if more ULXs beat with the pulse of dead stars. NuSTAR, a relatively small telescope, has thrown a big loop into the mystery of black holes.

Adapted from NASA press release.

An international team of astronomers has found a pulsating, dead star beaming with the energy of about 10 million suns. This is the brightest pulsar – a dense stellar remnant left over from a supernova explosion – ever recorded.

The true nature of ULXs has remained hidden since their discovery about 20 years agoAndy FabianNASA/JPL-Caltech

The text in this work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page. For image rights, please see the credits associated with each individual image.

Yes

NASA’s NuSTAR Telescope Discovers Shockingly Bright Dead Star

8 October 2014 - 5:00pm
Astronomers have found a pulsating, dead star beaming with the energy of about 10 million suns. This is the brightest pulsar – a dense stellar remnant left over from a supernova explosion – ever recorded. The discovery was made with NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR.

Inside exotic dead stars are piles of waffles

8 October 2014 - 4:00pm
Neutron stars are made of some of the densest and strongest material in the universe – and they may look like waffles on the inside






Lutetia's dark side hosts hidden crater

8 October 2014 - 10:38am
Grooves found on Lutetia, an asteroid encountered by ESA's Rosetta spacecraft, point to the existence of a large impact crater on the unseen side of the rocky world.

UK to open 'solar storm' centre

8 October 2014 - 6:08am
The UK Met Office formally opens its Space Weather Operations Centre on Wednesday, to lead the forecasting of the Sun’s disruptive effects on Earth.

Binary orbits as the driver of γ-ray emission and mass ejection in classical novae

8 October 2014 - 1:00am

Binary orbits as the driver of γ-ray emission and mass ejection in classical novae

Nature 514, 7522 (2014). doi:10.1038/nature13773

Authors: Laura Chomiuk, Justin D. Linford, Jun Yang, T. J. O’Brien, Zsolt Paragi, Amy J. Mioduszewski, R. J. Beswick, C. C. Cheung, Koji Mukai, Thomas Nelson, Valério A. R. M. Ribeiro, Michael P. Rupen, J. L. Sokoloski, Jennifer Weston, Yong Zheng, Michael F. Bode, Stewart Eyres, Nirupam Roy & Gregory B. Taylor

Classical novae are the most common astrophysical thermonuclear explosions, occurring on the surfaces of white dwarf stars accreting gas from companions in binary star systems. Novae typically expel about 10−4 solar masses of material at velocities exceeding 1,000 kilometres per second. However, the mechanism of mass ejection in novae is poorly understood, and could be dominated by the impulsive flash of thermonuclear energy, prolonged optically thick winds or binary interaction with the nova envelope. Classical novae are now routinely detected at gigaelectronvolt γ-ray wavelengths, suggesting that relativistic particles are accelerated by strong shocks in the ejecta. Here we report high-resolution radio imaging of the γ-ray-emitting nova V959 Mon. We find that its ejecta were shaped by the motion of the binary system: some gas was expelled rapidly along the poles as a wind from the white dwarf, while denser material drifted out along the equatorial plane, propelled by orbital motion. At the interface between the equatorial and polar regions, we observe synchrotron emission indicative of shocks and relativistic particle acceleration, thereby pinpointing the location of γ-ray production. Binary shaping of the nova ejecta and associated internal shocks are expected to be widespread among novae, explaining why many novae are γ-ray emitters.

A mass of less than 15 solar masses for the black hole in an ultraluminous X-ray source

8 October 2014 - 1:00am

A mass of less than 15 solar masses for the black hole in an ultraluminous X-ray source

Nature 514, 7521 (2014). doi:10.1038/nature13730

Authors: C. Motch, M. W. Pakull, R. Soria, F. Grisé & G. Pietrzyński

Most ultraluminous X-ray sources have a typical set of properties not seen in Galactic stellar-mass black holes. They have luminosities of more than 3 × 1039 ergs per second, unusually soft X-ray components (with a typical temperature of less than about 0.3 kiloelectronvolts) and a characteristic downturn in their spectra above about 5 kiloelectronvolts. Such puzzling properties have been interpreted either as evidence of intermediate-mass black holes or as emission from stellar-mass black holes accreting above their Eddington limit, analogous to some Galactic black holes at peak luminosity. Recently, a very soft X-ray spectrum was observed in a rare and transient stellar-mass black hole. Here we report that the X-ray source P13 in the galaxy NGC 7793 is in a binary system with a period of about 64 days and exhibits all three canonical properties of ultraluminous sources. By modelling the strong optical and ultraviolet modulations arising from X-ray heating of the B9Ia donor star, we constrain the black hole mass to be less than 15 solar masses. Our results demonstrate that in P13, soft thermal emission and spectral curvature are indeed signatures of supercritical accretion. By analogy, ultraluminous X-ray sources with similar X-ray spectra and luminosities of up to a few times 1040 ergs per second can be explained by supercritical accretion onto massive stellar-mass black holes.

Ultraluminous X-ray sources: Small field with a large impact

8 October 2014 - 1:00am

Ultraluminous X-ray sources: Small field with a large impact

Nature 514, 7521 (2014). doi:10.1038/514171a

Authors: Jeanette C. Gladstone

The nature of ultraluminous X-ray astronomical sources has long been unclear. The latest observations of these rare systems provide some crucial clues, but still leave theorists scratching their heads. See Letters p.198 & p.202

An ultraluminous X-ray source powered by an accreting neutron star

8 October 2014 - 1:00am

An ultraluminous X-ray source powered by an accreting neutron star

Nature 514, 7521 (2014). doi:10.1038/nature13791

Authors: M. Bachetti, F. A. Harrison, D. J. Walton, B. W. Grefenstette, D. Chakrabarty, F. Fürst, D. Barret, A. Beloborodov, S. E. Boggs, F. E. Christensen, W. W. Craig, A. C. Fabian, C. J. Hailey, A. Hornschemeier, V. Kaspi, S. R. Kulkarni, T. Maccarone, J. M. Miller, V. Rana, D. Stern, S. P. Tendulkar, J. Tomsick, N. A. Webb & W. W. Zhang

The majority of ultraluminous X-ray sources are point sources that are spatially offset from the nuclei of nearby galaxies and whose X-ray luminosities exceed the theoretical maximum for spherical infall (the Eddington limit) onto stellar-mass black holes. Their X-ray luminosities in the 0.5–10 kiloelectronvolt energy band range from 1039 to 1041 ergs per second. Because higher masses imply less extreme ratios of the luminosity to the isotropic Eddington limit, theoretical models have focused on black hole rather than neutron star systems. The most challenging sources to explain are those at the luminous end of the range (more than 1040 ergs per second), which require black hole masses of 50–100 times the solar value or significant departures from the standard thin disk accretion that powers bright Galactic X-ray binaries, or both. Here we report broadband X-ray observations of the nuclear region of the galaxy M82 that reveal pulsations with an average period of 1.37 seconds and a 2.5-day sinusoidal modulation. The pulsations result from the rotation of a magnetized neutron star, and the modulation arises from its binary orbit. The pulsed flux alone corresponds to an X-ray luminosity in the 3–30 kiloelectronvolt range of 4.9 × 1039 ergs per second. The pulsating source is spatially coincident with a variable source that can reach an X-ray luminosity in the 0.3–10 kiloelectronvolt range of 1.8 × 1040 ergs per second. This association implies a luminosity of about 100 times the Eddington limit for a 1.4-solar-mass object, or more than ten times brighter than any known accreting pulsar. This implies that neutron stars may not be rare in the ultraluminous X-ray population, and it challenges physical models for the accretion of matter onto magnetized compact objects.

Moon water blew in on solar wind

7 October 2014 - 6:22pm
A fresh analysis of Apollo moon samples suggests that most of the moon's surface water came from interactions with the solar wind, not from comets and meteorites as was once believed






Super-close supernova used to map the Cigar Galaxy

7 October 2014 - 3:46pm
Astronomers are using echoes of light from the second-closest supernova ever recorded to build a 3D map of its host galaxy