Institute of Astronomy

Astronomy News

First evidence of icy comets orbiting a sun-like star

20 May 2016 - 9:19am

An international team of astronomers have found evidence of ice and comets orbiting a nearby sun-like star, which could give a glimpse into how our own solar system developed.

Using data from the Atacama Large Millimeter Array (ALMA), the researchers, led by the University of Cambridge, detected very low levels of carbon monoxide gas around the star, in amounts that are consistent with the comets in our own solar system.

The results, which will be presented today at the ‘Resolving Planet Formation in the era of ALMA and extreme AO’ conference in Santiago, Chile, are a first step in establishing the properties of comet clouds around sun-like stars just after the time of their birth.

Comets are essentially ‘dirty snowballs’ of ice and rock, sometimes with a tail of dust and evaporating ice trailing behind them, and are formed early in the development of stellar systems. They are typically found in the outer reaches of our solar system, but become most clearly visible when they visit the inner regions. For example, Halley’s Comet visits the inner solar system every 75 years, some take as long as 100,000 years between visits, and others only visit once before being thrown out into interstellar space.

It’s believed that when our solar system was first formed, the Earth was a rocky wasteland, similar to how Mars is today, and that as comets collided with the young planet, they brought many elements and compounds, including water, along with them.

The star in this study, HD 181327, has a mass about 30% greater than the sun and is located 160 light years away in the Painter constellation. The system is about 23 million years old, whereas our solar system is 4.6 billion years old.

“Young systems such as this one are very active, with comets and asteroids slamming into each other and into planets,” said Sebastián Marino, a PhD student from Cambridge’s Institute of Astronomy and the paper’s lead author. “The system has a similar ice composition to our own, so it’s a good one to study in order to learn what our solar system looked like early in its existence.”

Using ALMA, the astronomers observed the star, which is surrounded by a ring of dust caused by the collisions of comets, asteroids and other bodies. It’s likely that this star has planets in orbit around it, but they are impossible to detect using current telescopes.

“Assuming there are planets orbiting this star, they would likely have already formed, but the only way to see them would be through direct imaging, which at the moment can only be used for very large planets like Jupiter,” said co-author Luca Matrà, also a PhD student at Cambridge’s Institute of Astronomy.

In order to detect the possible presence of comets, the researchers used ALMA to search for signatures of gas, since the same collisions which caused the dust ring to form should also cause the release of gas. Until now, such gas has only been detected around a few stars, all substantially more massive than the sun. Using simulations to model the composition of the system, they were able to increase the signal to noise ratio in the ALMA data, and detect very low levels of carbon monoxide gas.

“This is the lowest gas concentration ever detected in a belt of asteroids and comets – we’re really pushing ALMA to its limits,” said Marino.

“The amount of gas we detected is analogous to a 200 kilometre diameter ice ball, which is impressive considering how far away the star is,” said Matrà. “It’s amazing that we can do this with exoplanetary systems now.”

The results have been accepted for publication in the Monthly Notices of the Royal Astronomical Society.

Reference:
S. Marino et al. ‘Exocometary gas in the HD 181327 debris ring.’ Paper presented to the Resolving Planet Formation in the era of ALMA and extreme AO conference, Santiago, May 16-20, 2016. http://www.eso.org/sci/meetings/2016/Planet-Formation2016/program.html

Inset image: ALMA image of the ring of comets around HD 181327 (colours have been changed). The white contours represent the size of the Kuiper Belt in the Solar System. Credit: Amanda Smith, University of Cambridge.

Astronomers have found the first evidence of comets around a star similar to the sun, providing an opportunity to study what our solar system was like as a ‘baby’.

The system has a similar ice composition to our own, so it’s a good one to study in order to learn what our solar system looked like early in its existence.Sebastián MarinoAmanda Smith, University of CambridgeIllustration of the dust ring surrounding HD 181327


The text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Evidence of ancient tsunamis on Mars

20 May 2016 - 9:10am

Scientists suggest that at least two huge tsunamis once swept across the Red Planet, triggered by large impacts.

A Beautiful Instance of Stellar Ornamentation

19 May 2016 - 9:15am
In this image from ESO’s Very Large Telescope (VLT), light from blazing blue stars energises the gas left over from the stars’ recent formation. The result is a strikingly colourful emission nebula, called LHA 120-N55, in which the stars are adorned with a mantle of glowing gas. Astronomers study these beautiful displays to learn about the conditions in places where new stars develop.

Astrophysics: Illuminating brown dwarfs

19 May 2016 - 9:12am

Astrophysics: Illuminating brown dwarfs

Nature 533, 7603 (2016). doi:10.1038/533330a

Authors: Adam P. Showman

Objects known as brown dwarfs are midway between stars and planets in mass. Observations of a hot brown dwarf irradiated by a nearby star will help to fill a gap in our knowledge of the atmospheres of fluid planetary objects. See Letter p.366

Astronomy: Black hole weighed with precision

19 May 2016 - 9:12am

Astronomy: Black hole weighed with precision

Nature 533, 7603 (2016). doi:10.1038/533294e

Astronomers have made precise measurements of the mass of a supermassive black hole.Aaron Barth of the University of California in Irvine focused the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile on the black hole at the heart of NGC 1332, a galaxy that is

An irradiated brown-dwarf companion to an accreting white dwarf

19 May 2016 - 9:11am

An irradiated brown-dwarf companion to an accreting white dwarf

Nature 533, 7603 (2016). doi:10.1038/nature17952

Authors: Juan V. Hernández Santisteban, Christian Knigge, Stuart P. Littlefair, Rene P. Breton, Vikram S. Dhillon, Boris T. Gänsicke, Thomas R. Marsh, Magaretha L. Pretorius, John Southworth & Peter H. Hauschildt

Interacting compact binary systems provide a natural laboratory in which to study irradiated substellar objects. As the mass-losing secondary (donor) in these systems makes a transition from the stellar to the substellar regime, it is also irradiated by the primary (compact accretor). The internal and external energy fluxes are both expected to be comparable in these objects, providing access to an unexplored irradiation regime. The atmospheric properties of donors are largely unknown, but could be modified by the irradiation. To constrain models of donor atmospheres, it is necessary to obtain accurate observational estimates of their physical properties (masses, radii, temperatures and albedos). Here we report the spectroscopic detection and characterization of an irradiated substellar donor in an accreting white-dwarf binary system. Our near-infrared observations allow us to determine a model-independent mass estimate for the donor of 0.055 ± 0.008 solar masses and an average spectral type of L1 ± 1, supporting both theoretical predictions and model-dependent observational constraints that suggest that the donor is a brown dwarf. Our time-resolved data also allow us to estimate the average irradiation-induced temperature difference between the dayside and nightside of the substellar donor (57 kelvin) and the maximum difference between the hottest and coolest parts of its surface (200 kelvin). The observations are well described by a simple geometric reprocessing model with a bolometric (Bond) albedo of less than 0.54 at the 2σ confidence level, consistent with high reprocessing efficiency, but poor lateral heat redistribution in the atmosphere of the brown-dwarf donor. These results add to our knowledge of binary evolution, in that the donor has survived the transition from the stellar to the substellar regime, and of substellar atmospheres, in that we have been able to test a regime in which the irradiation and the internal energy of a brown dwarf are comparable.

Astrophysics: Model predicts neutron-star signal

19 May 2016 - 9:11am

Astrophysics: Model predicts neutron-star signal

Nature 533, 7603 (2016). doi:10.1038/533294c

Physicists have devised a fast, accurate model that recreates the gravitational-wave signals produced by spiralling and colliding neutron stars. The model could help researchers to work out the stars' properties.The US Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) is looking for gravitational waves — ripples

VIDEO: Fireball captured on police dashcam

18 May 2016 - 9:11am

A bright fireball lit up the sky across several states in the US early on Tuesday - and was captured on a police officer's dashcam.

Time capsule galaxy can help probe conditions after the big bang

17 May 2016 - 9:43am

A galaxy with very low levels of heavy elements will enable astronomers to peer back in time

Identity-crisis comet may really be closest asteroid to the sun

17 May 2016 - 9:42am

Observations of a supposed comet that skirts close to the sun reveal it doesn't really act like one – so may be a different kind of space rock altogether

Discoverer of Neptune's rings dies

16 May 2016 - 9:08am

Andre Brahic, one of the people who discovered the rings of Neptune, has died aged 73, his publisher says.

Cannibal stars explode violently – as predicted by Darwin’s son

16 May 2016 - 9:07am

We now think one star swallowing another causes rare, bright red novae, but George Darwin had worked out the key details in the 19th century

Hubble Catches Views of a Jet Rotating with Comet 252P/LINEAR

13 May 2016 - 9:21am

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For thousands of years, humans have recorded sightings of mysterious comets sweeping across the nighttime skies. These celestial wanderers, "snowballs" of dust and ice, are swift-moving visitors from the cold depths of space. Some of them periodically visit the inner solar system during their journeys around the sun.

Unnamed dwarf planet may be third largest in the solar system

13 May 2016 - 9:19am

A body known only as 2007 OR10 has been given a boost by recent space telescope observations that peg it smaller than only Pluto and Eris

Temperate Earth-sized planets transiting a nearby ultracool dwarf star

12 May 2016 - 9:38am

Temperate Earth-sized planets transiting a nearby ultracool dwarf star

Nature 533, 7602 (2016). doi:10.1038/nature17448

Authors: Michaël Gillon, Emmanuël Jehin, Susan M. Lederer, Laetitia Delrez, Julien de Wit, Artem Burdanov, Valérie Van Grootel, Adam J. Burgasser, Amaury H. M. J. Triaud, Cyrielle Opitom, Brice-Olivier Demory, Devendra K. Sahu, Daniella Bardalez Gagliuffi, Pierre Magain & Didier Queloz

Star-like objects with effective temperatures of less than 2,700 kelvin are referred to as ‘ultracool dwarfs’. This heterogeneous group includes stars of extremely low mass as well as brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion), and represents about 15 per cent of the population of astronomical objects near the Sun. Core-accretion theory predicts that, given the small masses of these ultracool dwarfs, and the small sizes of their protoplanetary disks, there should be a large but hitherto undetected population of terrestrial planets orbiting them—ranging from metal-rich Mercury-sized planets to more hospitable volatile-rich Earth-sized planets. Here we report observations of three short-period Earth-sized planets transiting an ultracool dwarf star only 12 parsecs away. The inner two planets receive four times and two times the irradiation of Earth, respectively, placing them close to the inner edge of the habitable zone of the star. Our data suggest that 11 orbits remain possible for the third planet, the most likely resulting in irradiation significantly less than that received by Earth. The infrared brightness of the host star, combined with its Jupiter-like size, offers the possibility of thoroughly characterizing the components of this nearby planetary system.

Celestial mechanics: Fresh solutions to the four-body problem

12 May 2016 - 9:38am

Celestial mechanics: Fresh solutions to the four-body problem

Nature 533, 7602 (2016). doi:10.1038/nature17896

Authors: Douglas P. Hamilton

Describing the motion of three or more bodies under the influence of gravity is one of the toughest problems in astronomy. The report of solutions to a large subclass of the four-body problem is truly remarkable.

No Sun-like dynamo on the active star ζ Andromedae from starspot asymmetry

12 May 2016 - 9:37am

No Sun-like dynamo on the active star ζ Andromedae from starspot asymmetry

Nature 533, 7602 (2016). doi:10.1038/nature17444

Authors: R. M. Roettenbacher, J. D. Monnier, H. Korhonen, A. N. Aarnio, F. Baron, X. Che, R. O. Harmon, Zs. Kővári, S. Kraus, G. H. Schaefer, G. Torres, M. Zhao, T. A. ten Brummelaar, J. Sturmann & L. Sturmann

Sunspots are cool areas caused by strong surface magnetic fields that inhibit convection. Moreover, strong magnetic fields can alter the average atmospheric structure, degrading our ability to measure stellar masses and ages. Stars that are more active than the Sun have more and stronger dark spots than does the Sun, including on the rotational pole. Doppler imaging, which has so far produced the most detailed images of surface structures on other stars, cannot always distinguish the hemisphere in which the starspots are located, especially in the equatorial region and if the data quality is not optimal. This leads to problems in investigating the north–south distribution of starspot active latitudes (those latitudes with more starspot activity); this distribution is a crucial constraint of dynamo theory. Polar spots, whose existence is inferred from Doppler tomography, could plausibly be observational artefacts. Here we report imaging of the old, magnetically active star ζ Andromedae using long-baseline infrared interferometry. In our data, a dark polar spot is seen in each of two observation epochs, whereas lower-latitude spot structures in both hemispheres do not persist between observations, revealing global starspot asymmetries. The north–south symmetry of active latitudes observed on the Sun is absent on ζ And, which hosts global spot patterns that cannot be produced by solar-type dynamos.

Planetary science: Solar wind hits Pluto hard

12 May 2016 - 9:36am

Planetary science: Solar wind hits Pluto hard

Nature 533, 7602 (2016). doi:10.1038/533148a

The solar wind is diverted by Pluto, suggesting that, like some larger planets, the dwarf planet has a shield against the stream of energized particles emanating from the Sun.Before NASA's New Horizons spacecraft visited the dwarf planet (pictured) in 2015, most scientists thought that

Planetary science: Planet 9 may glow from within

12 May 2016 - 9:35am

Planetary science: Planet 9 may glow from within

Nature 533, 7602 (2016). doi:10.1038/533149d

The hypothetical ninth planet of the Solar System could shine brightly.Planet 9, if it exists, is thought to be an ice planet that is slightly smaller than Neptune, orbiting in the far outer Solar System. Esther Linder and Christoph Mordasini of the University of

The rise and fall of Martian lakes

12 May 2016 - 9:24am

There is a wealth of evidence, collected over the past few decades, that suggests liquid water was abundant in the early history of Mars – one of our nearest and most studied neighbours. However, the size, evolution and duration of standing bodies of water, such as lakes, on Mars' surface are still a matter of great debate. A recent study, using data from several spacecraft operating at Mars, paints a detailed picture of the rise and fall of standing bodies of water in a region of Mars which once hosted one of its largest lakes.