Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Is the Sagittarius dwarf galaxy a debris of the Large Magellanic Cloud?

25.02.2002


The Sagittarius dwarf galaxy is our nearest neighbor. Yet it has been discovered only recently, in 1994, being hidden by the stars and dust in our own Galaxy, the Milky Way. It is however possible today to better know this companion galaxy, thanks to variable stars, the RR Lyrae, in which Sgr-dw is particularly rich. In a recent paper, Patrick Cseresnjes, from Paris Observatory, shows for the first time that Sgr-dw is not typical of other satellites of the Milky Way, but reveals instead striking similarities with the Large Magellanic Cloud. He proposes and argues for the astonishing and original scenario that both systems might share a common progenitor.



The Sagittarius dwarf galaxy (Sgr hereafter) is a most interesting object. Located at only 75 000 light-years from the Sun and 50 000 light-years from the Galactic Center, it is the nearest known satellite of the Milky Way. In spite of this proximity, Sgr has been discovered only in 1994 because it was hidden to us by foreground Galactic stars.

Sgr is now in process of being swallowed by our own Galaxy after complete disruption caused by Galactic tides, showing that at least part of the stellar Halo has formed from accretion of smaller constituents. However, we still lack a clear understanding of this galaxy because the high degree of contamination by foreground Galactic stars and the varying extinction make it almost impossible to get a clean sample of stars. Fortunately, Sgr contains a fair amount of RR Lyrae stars. These variable stars have characteristic light curves and can easily be detected and separated from Galactic stars. Indeed, once their type is identified by their light curve, their absolute luminosity is derived, and the measure of their apparent luminosity gives their distance.


Using two series of photographic plates, taken at La Silla (European Southern Observatory) and digitized by the MAMA (operated at the Centre d’Analyse des Images, Observatoire de Paris), Patrick Cseresnjes and his collaborators detected about 2000 RR Lyrae stars in Sgr spread over 50 square degrees. The spatial distribution of these stars allows to map the northern extension of Sgr, where the Galactic stars outnumber those of Sgr by a factor up to a thousand. Compared to other satellites of the Milky Way, Sgr seems to be much more massive and extended.

Stellar evolution theory indicates that RR Lyraes are more than 10 Gigayears old. A catalogue of such stars offers therefore an unique opportunity to determine the progenitor of Sgr. The most obvious information available is the period which is very accurate and independent of crowding and extinction, allowing robust comparisons between different systems. Patrick Cseresnjes and his collaborators compared the period distribution of RR Lyrae stars in Sgr with those of all other dwarf galaxies with a known RR Lyrae population. The similarity with the Large Magellanic Cloud (LMC) clearly stands out. This similarity is even more striking when one considers that there are no two other couple of distributions showing such a high correlation. Statistical tests show that an identical parent distribution for Sgr and the LMC cannot be ruled out, in spite of the high resolution provided by the large size of the samples in both systems.

The similarity between Sgr and the LMC is not restricted to RR Lyrae stars, but has also been observed through other populations like Carbon stars, in 1998 or Red Giant Branch stars, in 2001. These similarities strongly suggest that both systems have similar stellar populations. So, Sgr could be a debris pulled out of the LMC after a collision and has been injected on its present orbit only recently. Possible configurations are a collision between the LMC and the Galaxy or the Small Magellanic Cloud.

This scenario, though attractive, raises many questions which need to be addressed. When did the collision occur? What happened to the gas? How can the present orbital planes of Sgr and the LMC seem to be perpendicular to each other? Future numerical simulations will assess the feasibility of this scenario.

Patrick Cseresnjes | alphagalileo

More articles from Physics and Astronomy:

nachricht Researchers demonstrate three-dimensional quantum hall effect for the first time
19.08.2019 | Singapore University of Technology and Design

nachricht A laser for penetrating waves
19.08.2019 | Helmholtz-Zentrum Dresden-Rossendorf

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A miniature stretchable pump for the next generation of soft robots

Soft robots have a distinct advantage over their rigid forebears: they can adapt to complex environments, handle fragile objects and interact safely with humans. Made from silicone, rubber or other stretchable polymers, they are ideal for use in rehabilitation exoskeletons and robotic clothing. Soft bio-inspired robots could one day be deployed to explore remote or dangerous environments.

Most soft robots are actuated by rigid, noisy pumps that push fluids into the machines' moving parts. Because they are connected to these bulky pumps by tubes,...

Im Focus: Vehicle Emissions: New sensor technology to improve air quality in cities

Researchers at TU Graz are working together with European partners on new possibilities of measuring vehicle emissions.

Today, air pollution is one of the biggest challenges facing European cities. As part of the Horizon 2020 research project CARES (City Air Remote Emission...

Im Focus: Self healing robots that "feel pain"

Over the next three years, researchers from the Vrije Universiteit Brussel, University of Cambridge, École Supérieure de Physique et de Chimie Industrielles de la ville de Paris (ESPCI-Paris) and Empa will be working together with the Dutch Polymer manufacturer SupraPolix on the next generation of robots: (soft) robots that ‘feel pain’ and heal themselves. The partners can count on 3 million Euro in support from the European Commission.

Soon robots will not only be found in factories and laboratories, but will be assisting us in our immediate environment. They will help us in the household, to...

Im Focus: Scientists create the world's thinnest gold

Scientists at the University of Leeds have created a new form of gold which is just two atoms thick - the thinnest unsupported gold ever created.

The researchers measured the thickness of the gold to be 0.47 nanometres - that is one million times thinner than a human finger nail. The material is regarded...

Im Focus: Study on attosecond timescale casts new light on electron dynamics in transition metals

An international team of scientists involving the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) in Hamburg has unraveled the light-induced electron-localization dynamics in transition metals at the attosecond timescale. The team investigated for the first time the many-body electron dynamics in transition metals before thermalization sets in. Their work has now appeared in Nature Physics.

The researchers from ETH Zurich (Switzerland), the MPSD (Germany), the Center for Computational Sciences of University of Tsukuba (Japan) and the Center for...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

The power of thought – the key to success: CYBATHLON BCI Series 2019

16.08.2019 | Event News

4th Hybrid Materials and Structures 2020 28 - 29 April 2020, Karlsruhe, Germany

14.08.2019 | Event News

What will the digital city of the future look like? City Science Summit on 1st and 2nd October 2019 in Hamburg

12.08.2019 | Event News

 
Latest News

Stanford builds a heat shield just 10 atoms thick to protect electronic devices

19.08.2019 | Information Technology

Researchers demonstrate three-dimensional quantum hall effect for the first time

19.08.2019 | Physics and Astronomy

Catalysts for climate protection

19.08.2019 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>