Monster Star Is Born, Baby Is 100 Times More Massive Than Our Sun

The most massive and brightest stars in the galaxy form within cool and dark clouds but the process remains not just shrouded in dust, but also in mystery [1]. An international team of astronomers has now used ALMA to perform a microwave prenatal scan to get a clearer look at the formation of one such monster star that is located around 11 000 light-years away, in a cloud known as the Spitzer Dark Cloud (SDC) 335.579-0.292.

There are two theories on the formation of the most massive stars. One suggests that the parental dark cloud fragments, creating several small cores that collapse on their own and eventually form stars. The other is more dramatic: the entire cloud begins to collapse inwards, with material racing towards the cloud’s centre to form one or more massive behemoths there. A team led by Nicolas Peretto of CEA/AIM Paris-Saclay, France, and Cardiff University, UK, realised that ALMA was the perfect tool to help find out what was really happening.

SDC335.579-0.292 was first revealed as a dramatic environment of dark, dense filaments of gas and dust through observations with NASA’s Spitzer Space Telescope and ESA’s Herschel Space Observatory. Now the team has used the unique sensitivity of ALMA to look in detail at both the amount of dust and the motion of the gas moving around within the dark cloud — and they have found a true monster.
The researchers say their observations – to be published in the journal Astronomy and Astrophysics – reveal how matter is being dragged into the centre of the huge gaseous cloud by the gravitational pull of the forming star – or stars – along a number of dense threads or filaments.

This video starts with a view of the Milky Way and closes in on the constellation of Norma and one of the richest parts of the sky. We see many star clusters and glowing nebulae, but many objects of great interest are hidden by thick clouds of dust and can only be seen at longer wavelengths. The final part of the video shows a new view of the dark cloud SDC 335.579-0.292 using the Atacama Large Millimeter/submillimeter array (ALMA). These observations have given astronomers the best view yet of a monster star in the process of forming.

Credit: ESO/Nick Risinger (skysurvey.org), DSS, ALMA(ESO/NAOJ/NRAO), NASA/JPL-Caltech/GLIMPSE. Music: movetwo

“The remarkable observations from ALMA allowed us to get the first really in-depth look at what was going on within this cloud,” said lead author Dr Nicolas Peretto, from Cardiff University. “We wanted to see how monster stars form and grow, and we certainly achieved our aim. One of the sources we have found is an absolute giant — the largest protostellar core ever spotted in the Milky Way!

“Even though we already believed that the region was a good candidate for being a massive star-forming cloud, we were not expecting to find such a massive embryonic star at its centre. This cloud is expected to form at least one star 100 times more massive than the Sun and up to a million times brighter. Only about one in 10,000 of all the stars in the Milky Way reach that kind of mass.”

This composite shows the region around the massive star-forming region SDC 335.579-0.292 seen using NASA’s Spitzer Space Telescope and ALMA. The Spitzer view is at infrared wavelengths (3.6, 4.5 and 8.0 microns) and the ALMA view is at wavelengths around three millimetres. The yellow blob at the centre of the ALMA images is a stellar womb with over 500 times the mass than the Sun — the largest ever seen in the Milky Way. The embryonic star within is hungrily feeding on the material that is racing inwards. It is expected to give birth to a very brilliant star with up to 100 times the mass of the Sun.

Credit: ALMA (ESO/NAOJ/NRAO)/NASA/JPL-Caltech/GLIMPSE

Different theories exist as to how these massive stars form but the team’s findings lend weight to the idea that the entire cloud core begins to collapse inwards, with material raining in towards the centre to form one or more massive stars.

Co-author Professor Gary Fuller, from The University of Manchester, said: “Not only are these stars rare, but their births are extremely rapid and childhood short, so finding such a massive object so early in its evolution in our Galaxy is a spectacular result.

 

This wide-field view shows a region of sky in the southern constellation of Norma (The Carpenter’s Square). At the centre lies the massive star-forming region SDC 335.579-0.292, but this is too obscured by dust to be visible. This is also true for the filamentary network of dust and gas. The star cluster NGC 6134 appears at the lower right and at the upper left the very hot blue star HD 147937 and its surrounding ejected clouds can be seen. This view was created from images forming part of the Digitized Sky Survey 2.

Credit: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin

“Our observations reveal in superb detail the filamentary network of dust and gas flowing into the central compact region of the cloud and strongly support the theory of global collapse for the formation of massive stars.”

The University of Manchester hosts the Science and Technology Facilities Council (STFC)-funded support centre for UK astronomers using ALMA, where the observations were processed.

Team member Dr Ana Duarte-Cabral, from the Université de Bordeaux, said: “Matter is drawn into the centre of the cloud from all directions but the filaments are the regions around the star that contain the densest gas and dust and so these distinct patterns are generated.”

Dr Peretto added: “We managed to get these very detailed observations using only a fraction of ALMA’s ultimate potential. ALMA will definitely revolutionise our knowledge of star formation, solving some current problems, and certainly raising new ones.”