Institute of Astronomy

Astronomy News

Never-before-seen moon spotted around dwarf planet Makemake

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

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

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

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

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

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

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

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

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.

Upside-down lightning and mystery blue glimpses caught on film

27 April 2016 - 9:12am

Fantastical light shows go on above thunderclouds, full of little-studied phenomena like upside-down lightning. Now they've been snapped from Earth and the ISS

Beagle probe 'seen in sharper view'

27 April 2016 - 9:10am

Supporting evidence that the Beagle-2 probe is sitting intact on the surface of Mars has come from a new imaging technique developed by UCL scientists.

Cassini gears up for final fiery plunge into Saturn’s atmosphere

26 April 2016 - 9:20am

After more than a decade orbiting Saturn, Cassini is almost out of fuel. The craft's final daring mission looms – a fatal dive into the gas giant's atmosphere

New Herschel maps and catalogues reveal stellar nurseries across the Galactic Plane

25 April 2016 - 9:19am

ESA's Herschel mission releases today a series of unprecedented maps of star-forming hubs in the plane of our Milky Way galaxy. This is accompanied by a set of catalogues listing hundreds of thousands of compact sources that span all phases leading to the birth of stars in our Galaxy. These maps and catalogues will be very valuable resources for astronomers, to exploit scientifically and for planning follow-up studies of particularly interesting regions in the Galactic Plane.

First direct evidence of ancient Mars’s oxygen-rich atmosphere

25 April 2016 - 9:18am

Suspicions that Mars once had oxygen-rich air are backed by the NASA Curiosity rover's find of manganese oxide in surface rocks

Earth’s core is two-and-a-half years younger than its crust

25 April 2016 - 9:18am

We have long known that gravity makes the Earth's centre age more slowly than its surface – but the effect is much more pronounced than once thought

Hubble telescope catches stunning picture of the Bubble Nebula

22 April 2016 - 9:36am

NASA’s largest space observatory has taken a striking picture of a giant cosmic bubble to celebrate being in orbit for 26 years

Hubble captures birthday bubble [heic1608]

22 April 2016 - 9:18am

This new NASA/ESA Hubble Space Telescope image, released to celebrate Hubble's 26th year in orbit, captures in stunning clarity what looks like a gigantic cosmic soap bubble. The object, known as the Bubble Nebula, is in fact a cloud of gas and dust illuminated by the brilliant star within it. The vivid new portrait of this dramatic scene wins the Bubble Nebula a place in the exclusive Hubble hall of fame, following an impressive lineage of Hubble anniversary images.

Hubble Sees a Star 'Inflating' a Giant Bubble

22 April 2016 - 9:18am

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Twenty-six candles grace NASA's Hubble Space Telescope's birthday cake this year, and now one giant space "balloon" will add to the festivities. Just in time for the 26th anniversary of Hubble's launch on April 24, 1990, the telescope has photographed an enormous, balloon-like bubble being blown into space by a super-hot, massive star. Astronomers trained the iconic telescope on this colorful feature, called the Bubble Nebula, or NGC 7635. The bubble is 7 light-years across about one-and-a-half times the distance from our sun to its nearest stellar neighbor, Alpha Centauri. The Bubble Nebula lies 7,100 light-years from Earth in the constellation Cassiopeia.

A 17-billion-solar-mass black hole in a group galaxy with a diffuse core

21 April 2016 - 9:51am

A 17-billion-solar-mass black hole in a group galaxy with a diffuse core

Nature 532, 7599 (2016). doi:10.1038/nature17197

Authors: Jens Thomas, Chung-Pei Ma, Nicholas J. McConnell, Jenny E. Greene, John P. Blakeslee & Ryan Janish

Quasars are associated with and powered by the accretion of material onto massive black holes; the detection of highly luminous quasars with redshifts greater than z = 6 suggests that black holes of up to ten billion solar masses already existed 13 billion years ago. Two possible present-day ‘dormant’ descendants of this population of ‘active’ black holes have been found in the galaxies NGC 3842 and NGC 4889 at the centres of the Leo and Coma galaxy clusters, which together form the central region of the Great Wall—the largest local structure of galaxies. The most luminous quasars, however, are not confined to such high-density regions of the early Universe; yet dormant black holes of this high mass have not yet been found outside of modern-day rich clusters. Here we report observations of the stellar velocity distribution in the galaxy NGC 1600—a relatively isolated elliptical galaxy near the centre of a galaxy group at a distance of 64 megaparsecs from Earth. We use orbit superposition models to determine that the black hole at the centre of NGC 1600 has a mass of 17 billion solar masses. The spatial distribution of stars near the centre of NGC 1600 is rather diffuse. We find that the region of depleted stellar density in the cores of massive elliptical galaxies extends over the same radius as the gravitational sphere of influence of the central black holes, and interpret this as the dynamical imprint of the black holes.

Astronomy: Spinning black holes align

21 April 2016 - 9:50am

Astronomy: Spinning black holes align

Nature 532, 7599 (2016). doi:10.1038/532284b

Black holes at the cores of galaxies tend to spin in the same direction.This unexpected result comes from a survey of 65 galaxies in the same patch of sky by the Giant Metrewave Radio Telescope near Pune in India. Andrew Russ Taylor and Preshanth