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Resolved atomic lines reveal outflows in two ultraluminous X-ray sources

Astronomy News - 5 May 2016 - 9:45am

Resolved atomic lines reveal outflows in two ultraluminous X-ray sources

Nature 533, 7601 (2016). doi:10.1038/nature17417

Authors: Ciro Pinto, Matthew J. Middleton & Andrew C. Fabian

Ultraluminous X-ray sources are extragalactic, off-nucleus, point sources in galaxies, and have X-ray luminosities in excess of 3 × 1039 ergs per second. They are thought to be powered by accretion onto a compact object. Possible explanations include accretion onto neutron stars with strong magnetic fields, onto stellar-mass black holes (of up to 20 solar masses) at or in excess of the classical Eddington limit, or onto intermediate-mass black holes (103–105 solar masses). The lack of sufficient energy resolution in previous analyses has prevented an unambiguous identification of any emission or absorption lines in the X-ray band, thereby precluding a detailed analysis of the accretion flow. Here we report the presence of X-ray emission lines arising from highly ionized iron, oxygen and neon with a cumulative significance in excess of five standard deviations, together with blueshifted (about 0.2 times light velocity) absorption lines of similar significance, in the high-resolution X-ray spectra of the ultraluminous X-ray sources NGC 1313 X-1 and NGC 5408 X-1. The blueshifted absorption lines must occur in a fast-outflowing gas, whereas the emission lines originate in slow-moving gas around the source. We conclude that the compact object in each source is surrounded by powerful winds with an outflow velocity of about 0.2 times that of light, as predicted by models of accreting supermassive black holes and hyper-accreting stellar-mass black holes.

Software error doomed Japanese Hitomi spacecraft

Astronomy News - 5 May 2016 - 9:45am

Software error doomed Japanese Hitomi spacecraft

Nature 533, 7601 (2016).

Author: Alexandra Witze

Space agency declares the astronomy satellite a loss.

US and China eye up European gravitational-wave mission

Astronomy News - 5 May 2016 - 9:43am

US and China eye up European gravitational-wave mission

Nature 533, 7601 (2016).

Author: Elizabeth Gibney

Space-based detector draws interest, but regulatory hurdles might complicate a partnership.

Planetary science: Martian water on the boil

Astronomy News - 5 May 2016 - 9:42am

Planetary science: Martian water on the boil

Nature 533, 7601 (2016). doi:10.1038/533011b

Water boiling under Mars's thin atmosphere could explain some of the planet's puzzling geological features, such as gullies (pictured) and hillside streaks, which some scientists have attributed to liquid water flowing today.A team led by Marion Massé of the University of Nantes

Unexplained plume over Mars could be caused by solar outburst

Astronomy News - 5 May 2016 - 9:39am

Planetary scientists are struggling to figure out how a massive cloud appeared high above Mars in 2012, but now they may have an answer  

New exoplanet trio may have been dried out by fiery young star

Astronomy News - 5 May 2016 - 9:38am

Three recently discovered nearby exoplanets may not be as habitable as they first looked, as their hot young star could have left them high and dry

The 2016 Transit of Mercury

Astronomy News - 4 May 2016 - 9:28am

On May 9, 2016, they will see a strange spot on the sun--a dark circle moving across the solar disk. This is no ordinary sunspot. It's the planet Mercury, making a rare transit of the sun.

Unique Fragment from Earth’s Formation Returns after Billions of Years in Cold Storage

Astronomy News - 3 May 2016 - 9:40am
Astronomers have found a unique object that appears to be made of inner Solar System material from the time of Earth’s formation, which has been preserved in the Oort Cloud far from the Sun for billions of years. Observations with ESO’s Very Large Telescope, and the Canada France Hawai`i Telescope, show that C/2014 S3 (PANSTARRS) is the first object to be discovered on a long-period cometary orbit that has the characteristics of a pristine inner Solar System asteroid. It may provide important clues about how the Solar System formed.

Japanese satellite’s death spiral linked to software malfunction

Astronomy News - 3 May 2016 - 9:39am

The Hitomi X-ray space telescope has failed just months after its launch, leaving astronomers hoping to glimpse black holes devastated

Strange Manx comet is time capsule from the early solar system

Astronomy News - 3 May 2016 - 9:38am

The tiny-tailed comet C/2014 S3 is a preserved piece of the original material that made the rocky planets, not a dirty snowball like its cometary siblings

Trio of Earth-sized planets around nearby star could reveal life

Astronomy News - 3 May 2016 - 9:36am

Astronomers have discovered three exoplanets in orbit around a nearby dwarf star, making them good targets for atmospheric analysis

Never-before-seen moon spotted around dwarf planet Makemake

Astronomy News - 29 April 2016 - 9:21am

Astronomers have previously looked for a satellite orbiting the Kuiper belt object and found nothing, so were surprised when one turned up

Milky Way’s nearest galaxies may be new to the neighbourhood

Astronomy News - 29 April 2016 - 9:21am

The Large and Small Magellanic Clouds have their stars all out of order, suggesting they only recently showed up on the Milky Way's doorstep

Japan to abandon space satellite forever

Astronomy News - 29 April 2016 - 9:18am

Japan's space agency says it will abandon efforts to restore a multimillion dollar satellite sent to explore black holes, after it spun out of control.

Powerful winds spotted from mysterious X-ray binaries

Astronomy News - 28 April 2016 - 10:08am

ESA's XMM-Newton has discovered gas streaming away at a quarter of the speed of light from very bright X-ray binaries in two nearby galaxies.

Astronomy: Dwarf dark galaxy leaves smudge

Astronomy News - 28 April 2016 - 10:03am

Astronomy: Dwarf dark galaxy leaves smudge

Nature 532, 7600 (2016). doi:10.1038/532416c

Astronomers have found an elusive type of miniature galaxy.Dwarf galaxies formed out of dark matter in the early Universe, but only a small number have been detected. Yashar Hezaveh of Stanford University in California and his colleagues studied images taken by the high-resolution Atacama

Four Lasers Over Paranal

Astronomy News - 28 April 2016 - 10:00am
On 26 April 2016 ESO’s Paranal Observatory in Chile hosted an event to mark the first light for the four powerful lasers that form a crucial part of the adaptive optics systems on ESO’s Very Large Telescope. Attendees were treated to a spectacular display of cutting-edge laser technology against the majestic skies of Paranal. These are the most powerful laser guide stars ever used for astronomy and the event marks the first use of multiple laser guide stars at ESO.

Winds a quarter the speed of light spotted leaving mysterious binary systems

Astronomy News - 28 April 2016 - 9:49am

Two black holes in nearby galaxies have been observed devouring their companion stars at a rate exceeding classically understood limits, and in the process, kicking out matter into surrounding space at astonishing speeds of around a quarter the speed of light.

The researchers, from the University of Cambridge, used data from the European Space Agency’s (ESA) XMM-Newton space observatory to reveal for the first time strong winds gusting at very high speeds from two mysterious sources of x-ray radiation. The discovery, published in the journal Nature, confirms that these sources conceal a compact object pulling in matter at extraordinarily high rates.

When observing the Universe at x-ray wavelengths, the celestial sky is dominated by two types of astronomical objects: supermassive black holes, sitting at the centres of large galaxies and ferociously devouring the material around them, and binary systems, consisting of a stellar remnant – a white dwarf, neutron star or black hole – feeding on gas from a companion star.

In both cases, the gas forms a swirling disc around the compact and very dense central object. Friction in the disc causes the gas to heat up and emit light at different wavelengths, with a peak in x-rays.

But an intermediate class of objects was discovered in the 1980s and is still not well understood. Ten to a hundred times brighter than ordinary x-ray binaries, these sources are nevertheless too faint to be linked to supermassive black holes, and in any case, are usually found far from the centre of their host galaxy.

“We think these so-called ‘ultra-luminous x-ray sources’ are special binary systems, sucking up gas at a much higher rate than an ordinary x-ray binary,” said Dr Ciro Pinto from Cambridge’s Institute of Astronomy, the paper’s lead author. “Some of these sources host highly magnetised neutron stars, while others might conceal the long-sought-after intermediate-mass black holes, which have masses around one thousand times the mass of the Sun. But in the majority of cases, the reason for their extreme behaviour is still unclear.”

Pinto and his colleagues collected several days’ worth of observations of three ultra-luminous x-ray sources, all located in nearby galaxies located less than 22 million light-years from the Milky Way. The data was obtained over several years with the Reflection Grating Spectrometer on XMM-Newton, which allowed the researchers to identify subtle features in the spectrum of the x-rays from the sources.

In all three sources, the scientists were able to identify x-ray emission from gas in the outer portions of the disc surrounding the central compact object, slowly flowing towards it.

But two of the three sources – known as NGC 1313 X-1 and NGC 5408 X-1 – also show clear signs of x-rays being absorbed by gas that is streaming away from the central source at 70,000 kilometres per second – almost a quarter of the speed of light.

“This is the first time we’ve seen winds streaming away from ultra-luminous x-ray sources,” said Pinto. “And the very high speed of these outflows is telling us something about the nature of the compact objects in these sources, which are frantically devouring matter.”

While the hot gas is pulled inwards by the central object's gravity, it also shines brightly, and the pressure exerted by the radiation pushes it outwards. This is a balancing act: the greater the mass, the faster it draws the surrounding gas; but this also causes the gas to heat up faster, emitting more light and increasing the pressure that blows the gas away.

There is a theoretical limit to how much matter can be pulled in by an object of a given mass, known as the Eddington limit. The limit was first calculated for stars by astronomer Arthur Eddington, but it can also be applied to compact objects like black holes and neutron stars.

Eddington’s calculation refers to an ideal case in which both the matter being accreted onto the central object and the radiation being emitted by it do so equally in all directions.

But the sources studied by Pinto and his collaborators are potentially being fed through a disc which has been puffed up due to internal pressures arising from the incredible rates of material passing through it. These thick discs can naturally exceed the Eddington limit and can even trap the radiation in a cone, making these sources appear brighter when we look straight at them. As the thick disc moves material further from the black hole's gravitational grasp it also gives rise to very high-speed winds like the ones observed by the Cambridge researchers.  

“By observing x-ray sources that are radiating beyond the Eddington limit, it is possible to study their accretion process in great detail, investigating by how much the limit can be exceeded and what exactly triggers the outflow of such powerful winds,” said Norbert Schartel, ESA XMM-Newton Project Scientist.

The nature of the compact objects hosted at the core of the two sources observed in this study is, however, still uncertain.

Based on the x-ray brightness, the scientists suspect that these mighty winds are driven from accretion flows onto either neutron stars or black holes, the latter with masses of several to a few dozen times that of the Sun.

To investigate further, the team is still scrutinising the data archive of XMM-Newton, searching for more sources of this type, and are also planning future observations, in x-rays as well as at optical and radio wavelengths.

“With a broader sample of sources and multi-wavelength observations, we hope to finally uncover the physical nature of these powerful, peculiar objects,” said Pinto.

C. Pinto et al. ‘Resolved atomic lines reveal outflows in two ultraluminous X-ray sources’ Nature (2016). DOI: 10.1038/nature17417.

Adapted from an ESA press release. 

Astronomers have observed two black holes in nearby galaxies devouring their companion stars at an extremely high rate, and spitting out matter at a quarter the speed of light.

This is the first time we’ve seen winds streaming away from ultra-luminous x-ray sources.Ciro PintoESA - C. CarreauArtist’s impression depicting a compact object – either a black hole or a neutron star – feeding on gas from a companion star in a binary system.

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


Profile of a methane sea on Titan

Astronomy News - 27 April 2016 - 9:14am

Saturn's largest moon is covered in seas and lakes of liquid hydrocarbons – and one sea has now been found to be filled with pure methane, with a seabed covered by a sludge of organic-rich material, and possibly surrounded by wetlands.

Hubble Discovers Moon Orbiting the Dwarf Planet Makemake

Astronomy News - 27 April 2016 - 9:14am

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Makemake is one of several dwarf planets that reside in the frigid outer realm of our solar system called the Kuiper Belt, a "junkyard" of countless icy bodies left over from our solar system's formation.