Subscribe to our free daily newsletters
. 24/7 Space News .




Subscribe to our free daily newsletters



STELLAR CHEMISTRY
Stellar motions in nearby galaxy hint at underlying dark matter
by Staff Writers
Paris (ESA) Nov 04, 2017


Sculptor dwarf galaxy

By pinning down, for the first time, the three-dimensional motions of individual stars in the nearby Sculptor dwarf galaxy, astronomers have shed new light on the distribution of invisible dark matter that pervades the galaxy. This study combined the positions of stars measured by ESA's Gaia mission with observations from the NASA/ESA Hubble Space Telescope taken twelve years earlier.

Our Milky Way galaxy, home to hundreds of billions of stars, is orbited by more than a dozen smaller satellite galaxies. The best known in this swarm, the Large and Small Magellanic Clouds, are visible with the naked eye from middle and southern latitudes, while the others are much fainter and can only be observed with the aid of telescopes.

These satellite galaxies are classed as dwarfs, since they contain only a small fraction of the stars hosted in regular galaxies. They are all engaged in gravitational interactions with the Milky Way, and these dynamical processes might leave telltale traces in their shape.

Astronomers have been studying stars in dwarf galaxies for decades, striving to reconstruct their origin and to uncover the past history of our Galaxy and its environment.

A new study has now brought one of these galaxies, the dwarf Sculptor, into unprecedented focus.

"For the first time, we've been able to determine how individual stars are moving through a dwarf satellite of our Milky Way," says Davide Massari from Kapteyn Astronomical Institute in Groningen, The Netherlands, who is lead author of the paper published in Nature Astronomy.

"This was possible by combining the exceptionally accurate measurements of stellar positions from Gaia's first data release with equally outstanding observations taken over twelve years earlier by the Hubble Space Telescope."

As expected, the shifts in the star positions as observed on the plane of the sky - called proper motions - are tiny, even over the long time baseline between 2002, when the Hubble observations were performed, and the first set of publicly released Gaia data, gathered between 2014 and 2015.

"We couldn't wait to see whether the Gaia observations could be used to measure individual proper motions in another galaxy, so we were thrilled to see this was indeed possible," says Amina Helmi, a co-author of the study, also based at Kapteyn Astronomical Institute in Groningen.

Massari, Helmi and colleagues measured the proper motions of roughly a hundred stars in the Sculptor dwarf galaxy. For a smaller subset of ten stars, chosen among those with the smallest errors, the astronomers could also retrieve from the literature an estimate of the radial velocity, which quantifies the stellar motion along the line of sight.

Using the proper motion and radial velocity measurements, they were able to reconstruct how these stars move in three dimensions - the first time this was done for a dwarf galaxy.

Previous studies of stellar positions in this and other dwarf galaxies had enabled astronomers to determine the overall motion of these satellites around the Milky Way.

"Our study went beyond: joining these two exceptional data sets, we could for the first time extract information about both the dwarf galaxy's motion and about the motions of stars within it," explains Massari.

Stellar motions are especially useful because these can lead astronomers to something they cannot see: dark matter, an invisible component that is vastly more abundant than ordinary matter across the cosmos.

Still elusive to direct detection, the presence of dark matter can be inferred by its gravitational effect on the motion of other objects, like stars or galaxies.

"Dwarf spheroidal galaxies like Sculptor are some of the most dark matter dominated objects we know of in the Universe," says Helmi. "It's in these places that we can really 'see' this mysterious component at play."

The new data indicate that stars in the Sculptor dwarf galaxy move preferentially on elongated radial orbits. This is consistent with the distribution of dark matter in the galaxy being 'cuspy', meaning that its density increases towards the centre instead of flattening out.

"Cuspy profiles are predicted by simulations of the large-scale distribution of dark matter within the standard cosmological scenario, and our new results are definitely in agreement with that," adds Helmi.

While the findings seem promising, the data sample used in this study is not very large, and more data are needed to place stronger constraints on the dark matter distribution in this galaxy. Even though Gaia has measured thousands of stars in the field of Sculptor, in this study the astronomers could only determine the proper motions for those that had also been observed by Hubble, which looked at two small patches within the broader galaxy field.

Gaia, on the other hand, has been scanning the entire sky. As its operations are continuing, the astronomers are looking forward to the larger, more precise data sets that will be released in future years.

The second data release, based on data collected between 2014 and 2016 and planned for April 2018, will not only contain exquisitely accurate positions of more than one billion stars, but also proper motions. This release will not provide proper motion measurements for stars in dwarf galaxies like Sculptor with sufficient precision to investigate the motions of individual stars, but the measurements will be precise enough to study the bulk motion of the galaxy.

"The second Gaia data release can be used to accurately pin down the overall motion of Sculptor around the Milky Way, and measure the motion of other dwarf galaxies, too, to unprecedented precision," says Anthony Brown from Leiden University in The Netherlands, chair of the Gaia Data Processing and Analysis Consortium (DPAC) and a co-author of the paper.

"But it's the final release, based on several years of Gaia observations, that will reveal the individual proper motions of thousands of stars in the satellites of our Milky Way."

Last week, ESA approved an extension of Gaia operations for an additional 18 months, so it will keep scanning the sky until at least 2020. One of the key science drivers for the extension was the study of proper motions of stars in dwarf galaxies, which requires observations taken over as long a time baseline as possible.

"With Gaia, we are looking at our Galaxy and its neighbours 'in action', delving into the motions of stars, and unveiling their secrets," says Timo Prusti, Gaia project scientist at ESA.

"This study provides us with an amazing preview of the exciting science that can be done with the full Gaia catalogue."

Research Report: "3D motions in the Sculptor dwarf galaxy as a glimpse of a new era" by D. Massari, et al., is published in Nature Astronomy.

STELLAR CHEMISTRY
Dark matter and dark energy: do they really exist?
Geneva, Switzerland (SPX) Nov 23, 2017
A University of Geneva researcher has recently shown that the accelerating expansion of the universe and the movement of the stars in the galaxies can be explained without drawing on the concepts of dark matter and dark energy... which might not actually exist. For close on a century, researchers have hypothesised that the universe contains more matter than can be directly observed, known as "d ... read more

Related Links
Gaia at ESA
Stellar Chemistry, The Universe And All Within It


Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Contributor
$5 Billed Once


credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly


paypal only

Comment using your Disqus, Facebook, Google or Twitter login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

STELLAR CHEMISTRY
Building for a future in space: An interview with Dava Newman and Gui Trotti

Space Farms: 'Mark Watney in The Martian Was Right to Add Poop to the Soil'

NASA successfully fires Voyager 1 thrusters after 37 years

New motion sensors major step towards cheaper wearable technology

STELLAR CHEMISTRY
ISRO eyes one rocket launch a month in 2018

Russia to build launch pad for super heavy-lift carrier by 2028

Mechanisms are critical to all space vehicles

Russia loses contact with satellite after launch from new spaceport

STELLAR CHEMISTRY
Earthworms can reproduce in Mars-like soil

Opportunity Greets Winter Solstice

NASA builds its next Mars rover mission

Scientists developed a new sensor for future missions to the Moon and Mars

STELLAR CHEMISTRY
Nation 'leads world' in remote sensing technology

China plans for nuclear-powered interplanetary capacity by 2040

China plans first sea based launch by 2018

China's reusable spacecraft to be launched in 2020

STELLAR CHEMISTRY
Going green to the Red Planet

Orbital ATK purchase by Northrop Grumman approved by shareholders

UK space launch program receives funding boost from Westminster

Need to double number of operational satellites: ISRO chief

STELLAR CHEMISTRY
Quantum optics allows us to abandon expensive lasers in spectroscopy

Spin current from heat: New material increases efficiency

New catalyst controls activation of a carbon-hydrogen bond

Math gets real in strong, lightweight structures

STELLAR CHEMISTRY
Scientists identify key factors that help microbes thrive in harsh environments

Exoplanet Has Smothering Stratosphere Without Water

Scientists study Earth's earliest life forms in Nevada hot spring

Traces of life on nearest exoplanets may be hidden in equatorial trap

STELLAR CHEMISTRY
Pluto's hydrocarbon haze keeps dwarf planet colder than expected

Jupiter's Stunning Southern Hemisphere

Watching Jupiter's multiple pulsating X-ray Aurora

Help Nickname New Horizons' Next Flyby Target




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News






The content herein, unless otherwise known to be public domain, are Copyright 1995-2017 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement