Institute of Astronomy

Astronomy News

Astronomers Discover Rare Fossil Relic of Early Milky Way

8 September 2016 - 9:19am
Using ESO’s Very Large Telescope and other telescopes a fossilised remnant of the early Milky Way harbouring stars of hugely different ages has been revealed by an international team of astronomers. This stellar system resembles a globular cluster, but is like no other cluster known. It contains stars remarkably similar to the most ancient stars in the Milky Way and bridges the gap in understanding between our galaxy’s past and its present.

Massive holes ‘punched’ through a trail of stars likely caused by dark matter

7 September 2016 - 11:50am

Researchers have detected two massive holes which have been ‘punched’ through a stream of stars just outside the Milky Way, and found that they were likely caused by clumps of dark matter, the invisible substance which holds galaxies together and makes up a quarter of all matter and energy in the universe.

The scientists, from the University of Cambridge, found the holes by studying the distribution of stars in the Milky Way. While the clumps of dark matter that likely made the holes are gigantic in comparison to our Solar System – with a mass between one million and 100 million times that of the Sun – they are actually the tiniest clumps of dark matter detected to date.

The results, which have been submitted to the Monthly Notices of the Royal Astronomical Society, could help researchers understand the properties of dark matter, by inferring what type of particle this mysterious substance could be made of. According to their calculations and simulations, dark matter is likely made up of particles more massive and more sluggish than previously thought, although such a particle has yet to be discovered.

“While we do not yet understand what dark matter is formed of, we know that it is everywhere,” said Dr Denis Erkal from Cambridge’s Institute of Astronomy, the paper’s lead author. “It permeates the universe and acts as scaffolding around which astrophysical objects made of ordinary matter – such as galaxies – are assembled.”

Current theory on how the universe was formed predicts that many of these dark matter building blocks have been left unused, and there are possibly tens of thousands of small clumps of dark matter swarming in and around the Milky Way. These small clumps, known as dark matter sub-haloes, are completely dark, and don’t contain any stars, gas or dust.

Dark matter cannot be directly measured, and so its existence is usually inferred by the gravitational pull it exerts on other objects, such as by observing the movement of stars in a galaxy. But since sub-haloes don’t contain any ordinary matter, researchers need to develop alternative techniques in order to observe them.

The technique the Cambridge researchers developed was to essentially look for giant holes punched through a stream of stars. These streams are the remnants of small satellites, either dwarf galaxies or globular clusters, which were once in orbit around our own galaxy, but the strong tidal forces of the Milky Way have torn them apart. The remnants of these former satellites are often stretched out into long and narrow tails of stars, known as stellar streams.

“Stellar streams are actually simple and fragile structures,” said co-author Dr Sergey Koposov. “The stars in a stellar stream closely follow one another since their orbits all started from the same place. But they don’t actually feel each other’s presence, and so the apparent coherence of the stream can be fractured if a massive body passes nearby. If a dark matter sub-halo passes through a stellar stream, the result will be a gap in the stream which is proportional to the mass of the body that created it.”

The researchers used data from the stellar streams in the Palomar 5 globular cluster to look for evidence of a sub-halo fly-by. Using a new modelling technique, they were able to observe the stream with greater precision than ever before. What they found was a pair of wrinkled tidal tails, with two gaps of different widths.

By running thousands of computer simulations, the researchers determined that the gaps were consistent with a fly-by of a dark matter sub-halo. If confirmed, these would be the smallest dark matter clumps detected to date.

“If dark matter can exist in clumps smaller than the smallest dwarf galaxy, then it also tells us something about the nature of the particles which dark matter is made of – namely that it must be made of very massive particles,” said co-author Dr Vasily Belokurov. “This would be a breakthrough in our understanding of dark matter.”

The reason that researchers can make this connection is that the mass of the smallest clump of dark matter is closely linked to the mass of the yet unknown particle that dark matter is composed of. More precisely, the smaller the clumps of dark matter, the higher the mass of the particle.

Since we do not yet know what dark matter is made of, the simplest way to characterise the particles is to assign them a particular energy or mass. If the particles are very light, then they can move and disperse into very large clumps. But if the particles are very massive, then they can’t move very fast, causing them to condense – in the first instance – into very small clumps.

“Mass is related to how fast these particles can move, and how fast they can move tells you about their size,” said Belokurov. “So that’s why it’s so interesting to detect very small clumps of dark matter, because it tells you that the dark matter particle itself must be very massive.”

“If our technique works as predicted, in the near future we will be able to use it to discover even smaller clumps of dark matter,” said Erkal. “It’s like putting dark matter goggles on and seeing thousands of dark clumps each more massive than a million suns whizzing around.”

Denis Erkal et al. ‘A sharper view of Pal 5s tails: Discovery of stream perturbations with a novel non-parametric technique.’ arXiv:1609.01282

The discovery of two massive holes punched through a stream of stars could help answer questions about the nature of dark matter, the mysterious substance holding galaxies together.

While we do not yet understand what dark matter is formed of, we know that it is everywhere.Denis ErkalV. Belokurov, D. Erkal, S.E. Koposov (IoA, Cambridge). Photo: Colour image of M31 from Adam Evans.Artist's impression of dark matter clumps around a Milky Way-like galaxy

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


NASA probe about to leave for asteroid Bennu and bring bits home

7 September 2016 - 11:49am

The OSIRIS-REx spacecraft will pioneer a new way to grab samples off an asteroid and then return them to Earth

Philae found!

6 September 2016 - 9:36am

Less than a month before the end of the mission, Rosetta's high-resolution camera has revealed the Philae lander wedged into a dark crack on Comet 67P/Churyumov-Gerasimenko.

NASA’s Juno probe snaps first images of Jupiter’s north pole

6 September 2016 - 9:34am

The images were captured during Juno’s first fly-by of the planet on 27 August when it was about 4200 kilometres above Jupiter’s clouds

Found: Philae lander finally spotted by Rosetta on comet 67P

6 September 2016 - 9:33am

With just weeks to go before the end of its mission, the European Space Agency's Rosetta spacecraft has found its lost companion, the Philae lander

New exoplanet think tank will ask the big questions about extra-terrestrial worlds

6 September 2016 - 9:30am

With funding from The Kavli Foundation, the think tank will bring together some of the major researchers in exoplanetary science – arguably the most exciting field in modern astronomy – for a series of annual meetings to address the biggest questions in this field which humanity could conceivably answer in the next decade.

“We’re really at the frontier in exoplanet research,” said Dr Nikku Madhusudhan of Cambridge’s Institute of Astronomy, who is leading the think tank. “The pace of new discoveries is incredible – it really feels like anything can be discovered any moment in our exploration of extra-terrestrial worlds. By bringing together some of the best minds in this field we aim to consolidate our collective wisdom and address the biggest questions in this field that humanity can ask and answer at this time.”

Tremendous advances have been made in the study of exoplanets since the first such planet was discovered around a sun-like star in 1995 by the Cavendish Laboratory’s Professor Didier Queloz. Just last month, a potentially habitable world was discovered in our own neighbourhood, orbiting Proxima Centauri, the nearest star to the sun.

However, there are still plenty questions to be answered, such as whether we’re capable of detecting signatures of life on other planets within the next ten years, what the best strategies are to find habitable planets, how diverse are planets and their atmospheres, and how planets form in the first place.

With at least four space missions and numerous large ground-based facilities scheduled to become operational in the next decade, exoplanetary scientists will be able to detect more and more exoplanets, and will also have the ability to conduct detailed studies of their atmospheres, interiors, and formation conditions. At the same time, major developments are expected in all aspects of exoplanetary theory and data interpretation.

In order to make these major advances in the field, new interdisciplinary approaches are required. Additionally, as new scientific questions and areas emerge at an increasingly fast pace, there is a need for a focused forum where emerging questions in frontier areas of the field can be discussed. “Given the exciting advancements in exoplanetary science now is the right time to assess the state of the field and the scientific challenges and opportunities on the horizon,” said Professor Andy Fabian, director of the Institute of Astronomy at Cambridge.

The think tank will operate in the form of a yearly Exoplanet Symposium series which will be focused on addressing pressing questions in exoplanetary science. One emerging area or theme in exoplanetary science will be chosen each year based on its critical importance to the advancement of the field, relevance to existing or imminent observational facilities, need for an interdisciplinary approach, and/or scope for fundamental breakthroughs.

About 30 experts in the field from around the world will discuss outstanding questions, new pathways, interdisciplinary synergies, and strategic actions that could benefit the exoplanet research community.

The inaugural symposium, “Kavli ExoFrontiers 2016”, is being held this week in Cambridge. The goal of this first symposium is to bring together experts from different areas of exoplanetary science to share their visions about the most pressing questions and future outlook of their respective areas. These visions will help provide both a broad outlook of the field and identify the ten most important questions in the field that could be addressed within the next decade. “We hope the think tank will provide a platform for new breakthroughs in the field through interdisciplinary and international efforts while bringing the most important scientific questions of our time to the fore,” said Madhusudhan. “We are in the golden age of exoplanetary science.”

More information about the Kavli ExoFrontiers 2016 Symposium is available at:

An international exoplanet ‘think tank’ is meeting this week in Cambridge to deliberate on the ten most important questions that humanity could answer in the next decade about planets outside our solar system.

We’re really at the frontier in exoplanet research.Nikku MadhusudhanESO/M. KornmesserArtist’s impression of the ultracool dwarf star TRAPPIST-1 from the surface of one of its planets

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


New images of Jupiter

6 September 2016 - 9:29am

NASA has released spectacular images of Jupiter that have never been seen before.

Philae: Lost comet lander is found

6 September 2016 - 9:28am

Europe's comet lander Philae, last seen in November 2014, has been identified in new pictures from the Rosetta probe.

Freddie Mercury: Asteroid named after late Queen star to mark 70th birthday

6 September 2016 - 9:27am

Freddie Mercury is honoured with an asteroid named after him to mark what would have been his 70th birthday.

Planet smash-up 'brought carbon to Earth'

6 September 2016 - 9:26am

Much of Earth's life-giving carbon could have been delivered in an asteroid collision about 4.4 billion years ago, a theory suggests.

Here’s what colourful clouds on alien gas giants would look like

5 September 2016 - 9:18am

If you could hover over hot Jupiters in a spaceship, you might see deep blue skies and bright clouds, depending on how closely the planets hug their suns

Call for media: First data release from ESA's Gaia mission

2 September 2016 - 9:41am

Media representatives are invited to a briefing on the first data release of ESA's Gaia mission, an astrometry mission to map the stars of our galaxy, the Milky Way.

Stars burning strangely make life in the multiverse more likely

2 September 2016 - 9:38am

Supporters of the multiverse often cite a specific reaction in stars that seems tuned for life, making our universe improbable – but now there’s a new idea

'Ring of fire': Moon passes before Sun

2 September 2016 - 9:37am

Thousands of people have watched the Moon pass in front of the Sun, to make a so-called "ring of fire".

Aggregate dust particles at comet 67P/Churyumov–Gerasimenko

1 September 2016 - 10:05am

Aggregate dust particles at comet 67P/Churyumov–Gerasimenko

Nature 537, 7618 (2016). doi:10.1038/nature19091

Authors: Mark S. Bentley, Roland Schmied, Thurid Mannel, Klaus Torkar, Harald Jeszenszky, Jens Romstedt, Anny-Chantal Levasseur-Regourd, Iris Weber, Elmar K. Jessberger, Pascale Ehrenfreund, Christian Koeberl & Ove Havnes

Comets are thought to preserve almost pristine dust particles, thus providing a unique sample of the properties of the early solar nebula. The microscopic properties of this dust played a key part in particle aggregation during the formation of the Solar System. Cometary dust was previously considered to comprise irregular, fluffy agglomerates on the basis of interpretations of remote observations in the visible and infrared and the study of chondritic porous interplanetary dust particles that were thought, but not proved, to originate in comets. Although the dust returned by an earlier mission has provided detailed mineralogy of particles from comet 81P/Wild, the fine-grained aggregate component was strongly modified during collection. Here we report in situ measurements of dust particles at comet 67P/Churyumov–Gerasimenko. The particles are aggregates of smaller, elongated grains, with structures at distinct sizes indicating hierarchical aggregation. Topographic images of selected dust particles with sizes of one micrometre to a few tens of micrometres show a variety of morphologies, including compact single grains and large porous aggregate particles, similar to chondritic porous interplanetary dust particles. The measured grain elongations are similar to the value inferred for interstellar dust and support the idea that such grains could represent a fraction of the building blocks of comets. In the subsequent growth phase, hierarchical agglomeration could be a dominant process and would produce aggregates that stick more easily at higher masses and velocities than homogeneous dust particles. The presence of hierarchical dust aggregates in the near-surface of the nucleus of comet 67P also provides a mechanism for lowering the tensile strength of the dust layer and aiding dust release.

Planetary science: Cometary dust under the microscope

1 September 2016 - 10:05am

Planetary science: Cometary dust under the microscope

Nature 537, 7618 (2016). doi:10.1038/537037a

Authors: Ludmilla Kolokolova

The Rosetta spacecraft made history by successfully orbiting a comet. Data from the craft now reveal the structure of the comet's dust particles, shedding light on the processes that form planetary systems. See Letter p.73

Gang of gas giants may have tilted distant planet system

1 September 2016 - 10:00am

Astronomers track down one of the planets behind the first misaligned solar system ever found

NASA Extends Contract for Hubble Space Telescope Mission Operations

1 September 2016 - 9:59am
NASA has awarded a contract extension to Lockheed Martin Space Systems Corporation (LMSSC) of Greenbelt, Maryland, to continue maintaining the health and safety of the agency’s Hubble Space Telescope observatory through the next phase of its science mission.

First stars formed even later than previously thought

1 September 2016 - 9:57am

ESA's Planck satellite has revealed that the first stars in the Universe started forming later than previous observations of the Cosmic Microwave Background indicated. This new analysis also shows that these stars were the only sources needed to account for reionising atoms in the cosmos, having completed half of this process when the Universe had reached an age of 700 million years.