Does the Gemini telescope see a star over 300 solar masses with Zorro?

At the beginning of the XX^e century the great physicist and astronomer british James Jeans discovered a relationship between the temperature and the density of a cloud of matter guessing when such a cloud becomes unstable and gravitationally collapses into stars. The calculations show that the jeans mass — the mass limit below which there is collapse for a temperature set of given densities — evolve with collapse. This is easy to understand since the density increases and the temperature also for a gas compressed by the collapse. As a result, the mass decreases with this collapse, causing a cloud to break up into smaller clouds that can also collapse.

For this reason, the stars in the galaxies are in fact born in groups by fragmentations, sometimes successive with the birth of binary systems more or less stable. Our Sun therefore probably for a time was part of such a system in a nursery of young stars today scattered in the Milky Way about 4.5 billion years ago.

In these nurseries, some of the stars formed are very massive and, according to the laws ofastrophysics stellar evolution, when they exceed the eight solar masses, they will end up exploding in supernovae only a few million years after their birth at most.

A few years ago, the telescope Hubble had allowed a dizzying zoom in the direction of the star cluster R136 which is about 160,000 light years from Earth in the center of the Tarantula Nebula in the Large Magellanic Clouda dwarf galaxy companion to the Milky Way.

Astronomers then discovered thestar probably the most massive known to date and it posed a problem for the theory of stellar structure by probably exceeding 300 solar masses. Futura had extensively expanded on the discovery of R136a1 in the previous article below.

Today, astronomers return to this star with an open-access article on arXiv which reports new observations of R136a1 but, this time, conducted from the ground with the Zorro instrument on the Gemini South Telescope at the Gemini International Observatory, operated by NSF’s NOIRLab.

A zoom on R136a1 with the speckle imaging technique

The R136 cluster was observed with a resolution superior to that of Hubble in space by correcting for the effects of turbulence of the’atmosphere earthly. For this, it was necessary to use an image processing technique based on the existence of the phenomenon of scab which was observed for the first time in optics around 1920 by the Nobel Prize winner physical Max von Laue.

The scabsor speckle (speckle in English), are the set of small rapidly fluctuating spots that appear in the texture snapshot of an image and give it a grainy appearance. Combined with adaptive optics, the technique ofspeckle imaging allowed to show that R136a1 was observed very close to other stars of its cluster so that its brightness intrinsic has been somewhat overestimated.

However, there is a well-calibrated power law linking the mass of a star to its intrinsic luminosity, it was therefore necessary to review the estimates of the mass of R136a1. Previous observations suggested that R136a1 had a mass between 250 and 320 times the mass of the Sun. New observations of Zorro now suggest that R136a1 is actually only 170 to 230 solar masses in size, which still qualifies it as the most massive star known, however.

” Our results show us that the most massive star we currently know is not as massive as we previously thought. This suggests that the upper limit of stellar masses could also be smaller than previously thought. », Explains in a press release from NOIRLab Venu M. Kalari, main author of the article announcing this result.

Also, if R136a1 is much less massive than previously thought, so could other giant stars. However, the death of stars of more than 150 times the mass of the Sun must be done in the form of pair-instability supernovaewhich could therefore be rarer than expected.

Mass record for star R136a1

Article of Laurent Sacco published on 07/22/2010

A consensus within the community of astrophysicistscarrying about 150 times the mass of the Sun the limit for the mass of a star, has just been shattered if we are to believe observations from theopen cluster RMC 136a made with the VLT and Hubble. A star of 265 times the mass of the Sun has just been observed there as well as others exceeding the previous limit.

A theory of the structure of stars has been available for several decades, explaining many of their characteristics. We thus know from the pioneering work of the astrophysicist Arthur Eddington that there is a maximum luminosity for a star of a given mass, beyond which the blast of its radiation flux causes the star to lose significant mass.

This limit therefore imposed constraints on the growth of the mass of a star by accretion, and some suspected it might even lead to a mass limit for stars in the Universe. In fact, observations for some time in the Milky Way did not show stars exceeding about 150 solar masses. A consensus based on these observations therefore reigned within the community of stellar astrophysicists. This mass must have been a good approximation of the maximum mass for a star.

However, a group of astronomers observing the stars of the open cluster RMC 136a, located inside the Tarantula Nebula, itself a member of the Large Magellanic Cloud, 165,000 light years from the Sun, has just discover several stars exceeding this mass limit!

By combining archival data from the Hubble Space Telescope and those provided by the Very Large Telescope (VLT), they thus estimated that the mass of the star R136a1, as currently observed, is about 265 times that of the Sun.

Given the fact that its luminosity, almost 10 million times greater than that of the Sun, must cause a significant loss of mass, when it was born, about a million years ago, its mass must have even exceeded 320 solar masses. Either way, it’s a record!

According to astronomers, if R136a1 replaced the Sun in our solar systemits radiation would be compared to the latter what it is compared to that of the full moon. Raphael Hirschi, one of the researchers who co-authored the article about this discovery, even specifies that for R136a1: “ Its large mass would reduce the duration Earth year to three weeks and it would shower the Earth with radiation ultraviolet incredibly intense, making life impossible on our planet “.

The massive stars discovered in the RMC 136a cluster have been discovered thanks to the extreme resolving power in infrared VLT instruments. In total, we now know four stars in RMC 136a (which has about 100,000).

According to another team member, Olivier Schnurr of theAstrophysical Institute Potsdam: “ Our discovery confirms the earlier view that there is an upper limit to the size of stars, however this limit increases by a factor of two to now reach 300 solar masses. »

It remains to understand the birth and destiny of these stars…

For astronomer Paul Crowther: Either they were born that big or smaller stars merged to produce these extreme cases “. With such a large mass, they should end up as a supernova, but instead of having a core that collapses into black holeit is likely that reactions not operating in stars below 150 solar masses will occur there.

Theoretical astrophysicists have for some time proposed that temperatures and energies enormous that will reign at the end of life in these stars will cause the formation of electron-positron pairs, making them unstable. A few supernova candidates exploding due to this instability have already been observed, such as for example NS 2007bi.

We are probably not yet at the end of our surprises with the stars. Some theorists have even recently proposed that some of them burn quarks.