Institute of Astronomy

Astronomy News

LIGO’s underdog cousin ready to enhance gravitational-wave hunt

9 February 2017 - 10:24am

LIGO’s underdog cousin ready to enhance gravitational-wave hunt

Nature 542, 7640 (2017). http://www.nature.com/doifinder/10.1038/542146a

Author: Davide Castelvecchi

It missed the historic discovery, but the Virgo lab in Italy is now primed to extend LIGO’s reach and precision.

Astronomy: A leisurely way to visit the stars

9 February 2017 - 10:24am

Astronomy: A leisurely way to visit the stars

Nature 542, 7640 (2017). doi:10.1038/542140c

Plans to explore the nearest star system rely on light sails — reflective panels that are propelled by light. These craft travel so fast that they will have little time to explore their destination, but altering the way the sails are used could help.An

A bridge of stars connects two dwarf galaxies

9 February 2017 - 10:08am

For the past 15 years, scientists have been eagerly anticipating the data from Gaia. The first portion of information from the satellite was released three months ago and is freely accessible to everyone. This dataset of unprecedented quality is a catalogue of the positions and brightness of a billion stars in our Milky Way galaxy and its environs.

What Gaia has sent to Earth is unique. The satellite’s angular resolution is similar to that of the Hubble Space Telescope, but given its greater field of view, it can cover the entire sky rather than a small portion of it. In fact, Gaia uses the largest number of pixels to take digital images of the sky for any space-borne instrument. Better still, the Observatory has not just one telescope but two, sharing the one metre wide focal plane.

Unlike typical telescopes, Gaia does not just point and stare: it constantly spins around its axis, sweeping the entire sky in less than a month. Therefore, it not only measures the instantaneous properties of the stars, but also tracks their changes over time. This provides a perfect opportunity for finding a variety of objects, for example stars that pulsate or explode - even if this is not what the satellite was primarily designed for.

The Cambridge team concentrated on the area around the Magellanic Clouds and used the Gaia data to pick out pulsating stars of a particular type: the so-called RR Lyrae, very old and chemically un-evolved. As these stars have been around since the earliest days of the Clouds’ existence, they offer an insight into the pair’s history. Studying the Large and Small Magellanic Clouds (LMC and SMC respectively) has always been difficult as they sprawl out over a large area. But with Gaia’s all-sky view, this has become a much easier task.

Around the Milky Way, the clouds are the brightest, and largest, examples of dwarf satellite galaxies. Known to humanity since the dawn of history (and to Europeans since their first voyages to the Southern hemisphere) the Magellanic Clouds have remained an enigma to date. Even though the clouds have been a constant fixture of the heavens, astronomers have only recently had the chance to study them in any detail.

The Magellanic Clouds can be seen just above the horizon and below the arc of the Milky Way - D Erkal

Whether the clouds fit the conventional theory of galaxy formation or not depends critically on their mass and the time of their first approach to the Milky Way. The researchers at Cambridge’s Institute of Astronomy found clues that could help answer both of these questions.

Firstly, the RR Lyrae stars detected by Gaia were used to trace the extent of the Large Magellanic Cloud. The LMC was found to possess a fuzzy low-luminosity ‘halo’ stretching as far as 20 degrees from its centre. The LMC would only be able to hold on to the stars at such large distances if it was substantially bigger than previously thought, totalling perhaps as much as a tenth of the mass of the entire Milky Way.

An accurate timing of the clouds’ arrival to the galaxy is impossible without knowledge of their orbits. Unfortunately, satellite orbits are difficult to measure: at large distances, the object’s motion in the sky is so minute that it is simply unobservable over a human lifespan. In the absence of an orbit, Dr Vasily Belokurov and colleagues found the next best thing: a stellar stream.

Streams of stars form when a satellite - a dwarf galaxy or a star cluster - starts to feel the tidal force of the body around which it orbits. The tides stretch the satellite in two directions: towards and away from the host. As a result, on the periphery of the satellite, two openings form: small regions where the gravitational pull of the satellite is balanced by the pull of the host. Satellite stars that enter these regions find it easy to leave the satellite altogether and start orbiting the host. Slowly, star after star abandons the satellite, leaving a luminous trace on the sky, and thus revealing the satellite’s orbit.

“Stellar streams around the Clouds were predicted but never observed,” explains Dr Belokurov. “Having marked the locations of the Gaia RR Lyrae on the sky, we were surprised to see a narrow bridge-like structure connecting the two clouds. We believe that at least in part this ‘bridge’ is composed of stars stripped from the Small Cloud by the Large. The rest may actually be the LMC stars pulled from it by the Milky Way.”

The researchers believe the RR Lyrae bridge will help to clarify the history of the interaction between the clouds and our galaxy.

"We have compared the shape and the exact position of the Gaia stellar bridge to the computer simulations of the Magellanic Clouds as they approach the Milky Way”, explains Dr Denis Erkal, a co-author of the study. "Many of the stars in the bridge appear to have been removed from the SMC in the most recent interaction, some 200 million years ago, when the dwarf galaxies passed relatively close by each other. “We believe that as a result of that fly-by, not only the stars but also hydrogen gas was removed from the SMC. By measuring the offset between the RR Lyrae and hydrogen bridges, we can put constraints on the density of the gaseous Galactic corona.”

Composed of ionised gas at very low density, the hot Galactic corona is notoriously difficult to study. Nevertheless, it has been the subject of intense scrutiny because scientists believe it may contain most of the missing baryonic - or ordinary - matter. Astronomers are trying to estimate where this missing matter (the atoms and ions that make up stars, planets, dust and gas) is. It’s thought that most, or even all, of these missing baryons are in the corona. By measuring the coronal density at large distances they hope to solve this conundrum.

During the previous encounter between the Small and Large Magellanic Cloud, both stars and gas were ripped out of the Small Cloud, forming a tidal stream. Initially, the gas and stars were moving at the same speed. However, as the Clouds approached our Galaxy, the Milky Way’s corona exerted a drag force on both of them. The stars, being relatively small and dense, punched through the corona with no change in their speed. However, the more tenuous neutral hydrogen gas slowed down substantially in the corona. By comparing the current location of the stars and the gas, taking into account the density of the gas and how long the Clouds have spent in the corona, the team estimated the density of the corona. Dr. Erkal concludes, “Our estimate showed that the corona could make up a significant fraction of the missing baryons, in agreement with previous independent techniques. With the missing baryon problem seemingly alleviated, the current model of galaxy formation is holding up well to the increased scrutiny possible with Gaia.”

Reference
Vasily Belokurov et al. “Clouds, Streams and Bridges. Redrawing the blueprint of the Magellanic System with Gaia DR1”. Monthly Notices of the Royal Astronomical Society; 8th Feb. 2017; DOI:10.1093/mnras/stw3357

The Magellanic Clouds, the two largest satellite galaxies of the Milky Way, appear to be connected by a bridge stretching across 43,000 light years, according to an international team of astronomers led by researchers from the University of Cambridge. The discovery is reported in the journal Monthly Notices of the Royal Astronomical Society (MNRAS) and is based on the Galactic stellar census being conducted by the European Space Observatory, Gaia.

We believe that at least in part this 'bridge' is composed of stars stripped from the Small Cloud by the LargeVasily BelokurovV Belokurov, D Erkal, A MellingerPale white veils and the narrow bridge between the clouds represent the distribution of the RR Lyrae stars


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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Rare mid-weight black hole found at heart of bright star cluster

9 February 2017 - 10:07am

Intermediate-mass black holes – weighing a few hundred to a few thousand solar masses – are the Bigfoot of astronomy, but now we may have seen one in our galaxy

Glass from nuclear test site shows the moon was born dry

9 February 2017 - 10:07am

Examining residue from the first detonation of a nuclear weapon has helped explain why the moon seems to have so few volatile elements like water and methane

Gravitational wave detector prepares to peer into bizarre stars

8 February 2017 - 9:26am

It has already made the discovery of the decade – next LIGO aims to model weird events so we can recognise them when they arrive

Starlight test shows quantum world has been weird for 600 years

8 February 2017 - 9:26am

Unknown physics that could undermine quantum theory has been ruled out in a measurement guided by starlight emitted at least six centuries ago

First Euclid flight hardware delivered

8 February 2017 - 9:24am
An important milestone has been passed in the development of Euclid, a pioneering ESA mission to observe billions of faint galaxies and investigate the nature of dark matter and dark energy. The first flight hardware, in the form of four detectors known as Charge Coupled Devices (CCDs), has been delivered to Mullard Space Science Laboratory (MSSL) by UK company e2v. The remaining flight CCDs (36 in total) for the visible imager (VIS) will be delivered to MSSL by June.

Call for nominations for the JWST user committee (JSTUC)

8 February 2017 - 9:24am
STScI has issued a call for expressions of interest from community members who would like to serve as members of the James Webb Space Telescope Users Committee (JSTUC). At least two members of JSTUC will be astronomers from ESA member states. The deadline for receipt of nominations is 14 February 2017.

Sun’s rotation is slowed down by its own photons

6 February 2017 - 9:20am

The sun's layers slow the escape of photons of sunlight, and when they finally stream away they return the favour by slowing the rotation of its outer layer

Galactic X-rays could point way to dark matter

3 February 2017 - 9:12am

A small but distinctive signal in X-rays from the Milky Way could be key to proving the existence of dark matter.

Scientists record breach in magnetic field

3 February 2017 - 9:12am

Scientists in India have recorded the events that unfolded after the Earth's magnetic shield was breached.

Vera Rubin (1928–2016)

2 February 2017 - 1:38pm

Vera Rubin (1928–2016)

Nature 542, 7639 (2017). doi:10.1038/542032a

Author: Neta A. Bahcall

Observational astronomer who confirmed the existence of dark matter.

How to reach a planet 40 trillion kilometres away

2 February 2017 - 1:36pm

How to reach a planet 40 trillion kilometres away

Nature 542, 7639 (2017). http://www.nature.com/doifinder/10.1038/542020a

Author: Gabriel Popkin

A wild plan is taking shape to visit the nearest planet outside our Solar System. Here’s how we could get to Proxima b.

Astronomers explore uses for AI-generated images

2 February 2017 - 1:35pm

Astronomers explore uses for AI-generated images

Nature 542, 7639 (2017). http://www.nature.com/doifinder/10.1038/542016a

Author: Davide Castelvecchi

Neural networks produce pictures to train image-recognition programs and scientific software.

Planetary science: Pluto's dark equator explained

2 February 2017 - 1:35pm

Planetary science: Pluto's dark equator explained

Nature 542, 7639 (2017). doi:10.1038/542008a

The cosmic impact that formed Pluto's moon Charon several billion years ago may also have created the dark regions seen at Pluto's equator (pictured).Scientists led by Yasuhito Sekine at the University of Tokyo ran laboratory experiments to see what might happen if a comet

Oxygen ions sent from Earth have been spotted on the moon

2 February 2017 - 9:56am

Earth’s magnetic field sends streams of oxygen ions towards the moon every month – and that could give us clues to our planet’s early atmosphere

Tiny spacecraft could brake at exoplanet using alien starlight

2 February 2017 - 9:55am

Lightweight solar sails could bring spacecraft to the nearest star in just 20 years – but hitting the brakes will be challenging. A new paper suggests using the stars themselves to park around their planets

Water spotted in the atmosphere of nearby hot Jupiter exoplanet

2 February 2017 - 9:55am

Astronomers have detected water vapour in the atmosphere of 51 Pegasi b – which lies just 50 light years away

Celestial Cat Meets Cosmic Lobster

2 February 2017 - 9:52am
Astronomers have for a long time studied the glowing, cosmic clouds of gas and dust catalogued as NGC 6334 and NGC 6357, this gigantic new image from ESO’s Very Large Telescope Survey Telescope being only the most recent one. With around two billion pixels this is one of the largest images ever released by ESO. The evocative shapes of the clouds have led to their memorable names: the Cat’s Paw Nebula and the Lobster Nebula, respectively.