Key to Planet Formation Discovered With 3-Year Hubble Study of a Crowded, Massive Young Star Cluster

Hubble Finds that “Distance” From the Brightest Stars is Key to Preserving Primordial Discs

The NASA/ESA Hubble Space Telescope was utilized to carry out a three-year research study of the crowded, enormous and young star cluster Westerlund 2. The research study discovered that the product surrounding stars near the cluster’s center is inexplicably without the big, thick clouds of dust that would be anticipated to end up being worlds in a couple of million years. Their lack is brought on by the cluster’s most enormous and brightest stars that wear down and distribute the discs of gas and dust of surrounding stars. This is the very first time that astronomers have actually examined a very thick star cluster to study which environments agree with to world development.

This time-domain research study from 2016 to 2019 looked for to examine the homes of stars throughout their early evolutionary stages and to trace the development of their circumstellar environments. Such research studies had actually formerly been restricted to the nearby, low-density, star-forming areas. Astronomers have actually now utilized the Hubble Space Telescope to extend this research study to the center of among the couple of young enormous clusters in the Milky Way, Westerlund 2, for the very first time.

This NASA/ESA Hubble Space Telescope picture of the cluster Westerlund 2 and its environments has actually been launched to commemorate Hubble’s 25th year in orbit and a quarter of a century of brand-new discoveries, spectacular images and impressive science. The image’s main area, consisting of the star cluster, mixes visible-light information taken by the Advanced Camera for Surveys and near-infrared direct exposures taken by the Wide Field Camera 3. The surrounding area is made up of visible-light observations taken by the Advanced Camera for Surveys. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team

Astronomers have actually now discovered that worlds have a difficult time forming in this main area of the cluster. The observations likewise expose that stars on the cluster’s periphery do have tremendous planet-forming dust clouds embedded in their discs. To describe why some stars in Westerlund 2 have a tough time forming worlds while others do not, scientists recommend this is mostly due to area. The most enormous and brightest stars in the cluster gather together in the core. Westerlund 2 includes a minimum of 37 exceptionally enormous stars, some weighing approximately 100 solar masses. Their blistering ultraviolet radiation and hurricane-like outstanding winds imitate blowtorches and wear down the discs around surrounding stars, distributing the huge dust clouds.

“Basically, if you have monster stars, their energy is going to alter the properties of the discs,” described lead scientist Elena Sabbi, of the Space Telescope Science Institute in Baltimore, U.S.A.. “You may still have a disc, but the stars change the composition of the dust in the discs, so it’s harder to create stable structures that will eventually lead to planets. We think the dust either evaporates away in 1 million years, or it changes in composition and size so dramatically that planets don’t have the building blocks to form.”

This video reveals a pan throughout the brand-new picture of star cluster Westerlund 2, taken by the NASA/ESA Hubble Space telescope and launched to commemorate its 25th year in orbit.

Westerlund 2 is a unique lab in which to study outstanding evolutionary procedures due to the fact that it’s reasonably neighboring, is rather young, and includes an abundant outstanding population. The cluster lives in an outstanding breeding place referred to as Gum 29, situated approximately 14 000 light-years away in the constellation of Carina (The Ship’s Keel). The outstanding nursery is hard to observe due to the fact that it is surrounded by dust, however Hubble’s Wide Field Camera 3 can peer through the dirty veil in near-infrared light, offering astronomers a clear view of the cluster. Hubble’s sharp vision was utilized to fix and study the thick concentration of stars in the main cluster.

“With an age of less than about two million years, Westerlund 2 harbors some of the most massive, and hottest, young stars in the Milky Way,” stated staff member Danny Lennon of the Instituto de Astrofísica de Canarias and the Universidad de La Laguna. “The ambient environment of this cluster is therefore constantly bombarded by strong stellar winds and ultraviolet radiation from these giants that have masses of up to 100 times that of the Sun.”

Sabbi and her group discovered that of the almost 5000 stars in Westerlund 2 with masses in between 0.1 and 5 times the Sun’s mass, 1500 of them reveal remarkable variations in their luminosity, which is frequently accepted as being because of the existence of big dirty structures and planetesimals. Orbiting product would momentarily obstruct a few of the starlight, triggering variations in brightness. However, Hubble just identified the signature of dust particles around stars outside the main area. They did not spot these dips in brightness in stars living within 4 light-years of the center.

This video reveals a flight through Hubble’s brand-new close-up view of star cluster Westerlund 2, launched to commemorate the telescope’s 25th year in orbit.

“We think they are planetesimals or structures in formation,” Sabbi described. “These could be the seeds that eventually lead to planets in more evolved systems. These are the systems we don’t see close to very massive stars. We see them only in systems outside the center.”

Thanks to Hubble, astronomers can now see how stars are accreting in environments that resemble the early Universe, where clusters were controlled by beast stars. So far, the very best understood neighboring outstanding environment which contains enormous stars is the starbirth area in the Orion Nebula. However, Westerlund 2 is a richer target due to the fact that of its bigger outstanding population.

“Westerlund 2 gives us much better statistics on how mass affects the evolution of stars, how rapidly they evolve, and we see the evolution of stellar discs and the importance of stellar feedback in modifying the properties of these systems,” stated Sabbi. “We can use all of this information to inform models of planet formation and stellar evolution.”

This image from the Digitized Sky Survey reveals star cluster Westerlund 2 and its environments. A brand-new picture of Westerlund 2 was launched to commemorate the 25th anniversary of the NASA/ESA Hubble Space Telescope. Credit: NASA, ESA, Digitized Sky Survey 2

This cluster will likewise be an exceptional target for follow-up observations with the upcoming NASA/ESA/CSA James Webb Space Telescope, an infrared observatory. Hubble has actually assisted astronomers determine the stars that have possible planetary structures. With the Webb telescope, scientists will have the ability to study which discs around stars are not accreting product and which discs still have product that might develop into worlds. Webb will likewise study the chemistry of the discs in various evolutionary stages and enjoy how they alter, to assist astronomers identify what function the environment plays in their development.

“A major conclusion of this work is that the powerful ultraviolet radiation of massive stars alters the discs around neighboring stars,” stated Lennon. “If this is confirmed with measurements by the James Webb Space Telescope, this result may also explain why planetary systems are rare in old massive globular clusters.”

Reference: “Time-domain Study of the Young Massive Cluster Westerlund 2 with the Hubble Space Telescope. I” by E. Sabbi, M. Gennaro1, J. Anderson, V. Bajaj, N. Bastian, J. S. Gallagher III, M. Gieles, D. J. Lennon, A. Nota, K. C. Sahu and P. Zeidler, 18 March 2020, The Astrophysical Journal.
DOI: 10.3847/1538-4357/ab7372