The Large Magellanic Cloud Large Magellanic Cloud or LMC) is regularly the subject of research and publications. It is a dwarf galaxy of type barred spiralbarred spiral (it was long believed that it was of an irregular type according to the classification of Edwin HubbleEdwin Hubble), belonging to the local Group and located in thesouthern hemispheresouthern hemispherewhich is still sometimes debated as to whether it is a satellite galaxy of the Milky Way, or not. It is in any case the third galaxy closest to the Milky Way, after the dwarf galaxies of the Great ChienChien and Sagittarius and the fourth most massive of the Local Group after the Andromeda galaxy (M31), the Milky Way and the Triangle galaxy (M33). Its diameter is approximately 14,000 light yearslight years and its distance from our Galaxy is estimated at around 163,000 light years, these figures varying depending on the research teams and over time.
Often, when it comes to talking about the LMC it is about the famous supernova SN 1987A which occurred as its name indicates in 1987 and which made it possible to validate some of the theoretical predictions concerning the supernovaesupernovae by detecting the flux of neutrinos expected for this kind of cosmic catastrophe.
The observations give us good reason to believe that the LMC interacts with the halo of gazgaz of the Milky Way in which it is speeding vitessevitesse. A team of researchers has just looked at this question again using the telescopetelescope Hubble. This resulted in a publication in theAstrophysical Journal Letters a freely accessible version of which can be found on arXiv.
Travel through the Large Magellanic Cloud, a satellite galaxy 160,000 light years from the Milky Way, thanks to observations from the ESA Herschel satellite in particular, and in the infrared. This journey is also an opportunity to cross the gas, dust and stars that make up the observable bulk of a galaxy. The colors used are not real, infrared being invisible, but nevertheless calibrated according to the brightness of the objects observed. Blue hues represent visible lights. The green and pinkish-red hues represent infrared. The yellow hues represent gas. © Novae Factory
A laboratory to study interactions between galaxies
Hubble has shown us for decades that there are collisions of galaxies in theUniverseUniverse and these collisions play a role in their evolution, especially when there is a fusionfusion between two big galaxies spiralesgalaxies spiraleswhich gives elliptical galaxieselliptical galaxieslike M87.
Due to its proximity to the Milky Way, its interaction with the LMC is in some ways a laboratory of choice to study more easily and more precisely what happens when two galaxies collide, whether this leads to a merger or more simply to currents ofstarsstars snatched by the tidal forcestidal forces when both starsstars brush against each other.
In the present case, to study the interaction between the LMC and the gas halo of mattermatter ordinary and dark matterdark matter surrounding the Milky Way, the astrophysicistsastrophysicists needed to make observations in part of the band of theultravioletultraviolet (90-320 nm), part accessible only in space and with the instruments of the Hubble telescopes, in particular the spectrographespectrographe cosmic origins (Cosmic Origins Spectrograph – COS).
Astronomer Remy Indebetouw describes the Magellanic Clouds, two fascinating dwarf galaxies that sit alongside our giant Milky Way. To obtain a fairly accurate French translation, click on the white rectangle at the bottom right. English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Automatically translate”. Choose “French”. © The National Radio Astronomy ObservatoryA. Angelich, NRAO/AUI/NSF; ESO/NASA/JPL-Caltech/M. Grain Fair/R. Hurt; ESO/S. Brunier; Robert Gendler/Josch Hambsch; David L. Nidever et al., NRAO/AUI/NSF & A. Mellinger, LAB Survey, Parkes Obs., Westerbork Obs., Arecibo Obs.; Gurtina Besla; ESO/C. Malin; NASA/ESA/STScI; NCSA/NASA/A. Kritsuk/M. Norman/A. Boley
The researchers took advantage of the intense ultraviolet radiation coming from 28 quasarsquasars shiny. Remember that quasars are active galactic nucleiactive galactic nuclei whoseenergyenergy comes from theaccretionaccretion material on supermassive black holessupermassive black holes in rotation, containing more than a million massesmasses solar. This radiation makes it possible to “see” the non-luminous baryonic gas of galactic halos indirectly thanks to theabsorptionabsorption background light from these quasars. In this case, COS was in this way able to estimate the speed of the gas around the LMC, which allowed astrophysicists to determine the size of the halo.
« It’s a fantastic example of the cutting-edge science still made possible by Hubble’s unique capabilities. This result gives us valuable new insights into the complex history of the Milky Way and its nearby satellite galaxies “, declared about this work, in an ESA press release, Carole Mundell, scientific director of theEuropean Space AgencyEuropean Space Agency.
Dynamic pressure stripping
Hubble data made it possible to study a phenomenon that is also found in galaxies loversgalaxies lovers and with other dwarf galaxies moving in the Milky Way’s halo and called stripping by pressionpression dynamic (ram pressure stripping, in English). It’s a bit like the effect of the flow ofairair that we perceive when we put our hand outside a carcar in movementmovement by one windowwindow open. In this case, the dynamic pressure will tend to blow the gas into the dwarf galaxies, which find themselves depleted. This effect is proportional to the square of the speed of movement of a galaxy in the middle of a halo and it is counteracted by its content and density of matter, whether baryonic and normal or in the form of dark matter. It creates a trail of gas that follows a dwarf galaxy, like the tail of a cometcomet.
In the case of galaxy clusters, this leads to what are called jellyfish galaxies, Jellyfish Galaxy in English. Several examples are known as ESO 137-001.
Re-explanation of the dynamics of dwarf galaxies located in the vicinity of the Milky Way. © Paris Observatory – PS, CNRS
In the case of the LMC, it now appears that its halo is about 50,000 light years across. This is about 10 times smaller than the halos of other galaxies of the same mass as the LMC. This is a surprise for astrophysicists, but it is fortunate because this compactness is information to elucidate certain details of the history of the LMC’s encounter with the Milky Way.
The scenario mentioned suggests that the LMC has just passed the point closest to its orbitorbit around our Galaxy and its mass, which represents 10% of the mass of the Milky Way, allowed it to keep part of its original gas.
« The LMC is a survivor. Even though it has lost a lot of its gas, it still has enough to continue forming new stars. New star formation regions can therefore still be created. A smaller galaxy wouldn’t have survived – there would be no gas, just a collection of aging red stars said in the ESA press release Andrew Fox of Aura/STScI for the European Space Agency in Baltimore – he was the principal investigator leading the LMC observations with Hubble.
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