The two magellanic clouds are galaxies close to our Milky Way but their Southern position inhibits viewing by Northern telescopes.
Both galaxies are classified as SB(s)m, or a 'modified' barred spiral galaxy.
Announced in 2006, measurements with the Hubble Space Telescope suggest the Large and Small Magellanic Clouds may be moving too fast to be orbiting the Milky Way.
In 2014, measurements from the Hubble Space Telescope made it possible to determine that the LMC has a rotation period of 250 million years.
From a space.com story about LMC:
By pointing NASA's Hubble Space Telescope toward the two clouds, scientists began to catch a glimpse of the objects' histories. "Hubble's biggest contribution is enabling us to clock how fast the Magellanic clouds are moving," said Gurtina Besla, a researcher at the University of Arizona who studies dwarf galaxies. In 2007, Besla overturned conventional wisdom when she suggested that the LMC and SMC were making their first orbit of our galaxy.
"They're moving too fast to have been long-term companions of the Milky Way," Besla said.
She used data from the European Space Agency's Gaia spacecraft to clock smaller, satellite galaxies orbiting the LMC, as well. And, understanding how these galaxies move has helped researchers better calculate the mass of the LMC. Current estimates put the LMC at about 100 billion times as massive as Earth's sun, or a quarter the mass of the Milky Way. Besla said this size means the LMC is about 10 times heavier than previously calculated.
NASA has a database in its MAGCMXBCAT 'catalog of high-mass X-ray binaries (HMXBs) in the Small and Large Magellanic Clouds (SMC and LMC). The aim of this catalog is to provide easy access to the basic information on the X-ray sources and their counterparts in other wavelength ranges (UV, optical, IR, radio). Most of the sources have been identified as Be/X-ray binaries. Some sources, however, are only tentatively identified as HMXBs on the basis of a transient character and/or a hard X-ray spectrum. Further identification in other wavelength bands is needed to finally determine the nature of these sources. In cases where there is some doubt about the high-mass nature of the X-ray binary this is mentioned.
Apparently every X-ray source in the magellanic clouds is a 'high-mass X-ray Binary.'
Be/X-ray binaries (BeXRBs) are a class of high-mass X-ray binaries that consist of a Be star and a neutron star. The neutron star is usually in a wide highly elliptical orbit around the Be star. The Be stellar wind forms a disk confined to a plane often different from the orbital plane of the neutron star. When the neutron star passes through the Be disk, it accretes a large mass of gas in a short time. As the gas falls onto the neutron star, a bright flare in hard X-rays is seen.
Cosmologists have advanced to this mechanism: a Be star provides the disk for the neutron star to move through. When this gas accelerates it flares in X-ray. I assume this accretion and flaring continues for millions of years.
Astronomers are always seeking the amount of mass in everything. The LMC just gained mass (10x). There is no defined criteria for defining the masses for each one of the binary in the BeXRB.
Astronomers follow a simple rule: every X-ray source is a black hole.
Some other details:
LMC distance 163 Kly
LMC red shift 0.00093 z or 278km/s
SMC distance 200 Kly
SMC red shift 0.000527 z or 158 km/s
Both LMC SMC are in a cloud of neutral hydrogen, with a bridge of hydrogen between them.
With Hubble Constant = 70 km/s / Mpc and these red shifts:
LMC distance is calculated at 13Mly, SMC distance is 7.37 Mly
Their current accepted distances come from Cepheids not the red shift:
Using this period-luminosity relation, in 1913 the distance to the SMC was first estimated by Ejnar Hertzsprung. First he measured thirteen nearby cepheid variables to find the absolute magnitude of a variable with a period of one day. By comparing this to the periodicity of the variables as measured by Leavitt, he was able to estimate a distance of 10,000 parsecs (30,000 light years) between the Sun and the SMC. This later proved to be a gross underestimate of the true distance, but it did demonstrate the potential usefulness of this technique.
When Hubble telescope provides resolution to individual stars the astronomers can ignore these red shifts. When an astronomer says 'too fast' the basis for that conclusion is not clear.
Astronomers are still learning about the magellanic clouds.
30 Doradus is a well known nebula in the LMC.
The star-forming region, 30 Doradus, is one of the largest located close to the Milky Way and is found in the neighboring galaxy, Large Magellanic Cloud. About 2,400 massive stars in the center of 30 Doradus, also known as the Tarantula Nebula, are producing intense radiation and powerful winds as they blow off material.
Multimillion-degree gas detected in X-rays by the Chandra X-ray Observatory comes from shock fronts - similar to sonic booms -formed by these stellar winds and by supernova explosions. This hot gas carves out gigantic bubbles in the surrounding cooler gas and dust.
I find the proliferation of black holes (in an ever expanding variety) embarrassing.
However, winds, shock fronts, sonic booms, hot gas carving bubbles, and multimillion-degree gas emitting X-rays are not believable either.
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