Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


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


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 Hope to discover sure signs of life on Mars? New research says look for the element vanadium
22.09.2017 | University of Kansas

nachricht Calculating quietness
22.09.2017 | Forschungszentrum MATHEON ECMath

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: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

All Focus news of the innovation-report >>>



Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

Latest News

Rainbow colors reveal cell history: Uncovering β-cell heterogeneity

22.09.2017 | Life Sciences

Penn first in world to treat patient with new radiation technology

22.09.2017 | Medical Engineering

Calculating quietness

22.09.2017 | Physics and Astronomy

More VideoLinks >>>