Astrónomos de la Universidad de Arizona han identificado una nueva clase de sistema estelar. La colección de estrellas azules, en su mayoría jóvenes, se ve aquí usando la cámara avanzada para sondeos del telescopio espacial Hubble. crédito: michael jones
Se cree que las estructuras estelares se crean cuando las galaxias chocan con gas caliente en un proceso que puede compararse con una caída de barriga en una piscina.
Astrónomos de la Universidad de Arizona han identificado cinco ejemplos de una nueva clase de sistema estelar. No son exactamente galaxias y solo existen de forma aislada.
Los nuevos sistemas estelares contienen solo estrellas azules jóvenes, que se distribuyen en un patrón irregular y parecen existir en un aislamiento sorprendente de cualquier posible galaxia madre.
Los sistemas estelares, que los astrónomos dicen que aparecen a través de un telescopio como «gotas azules» y son del tamaño de pequeñas galaxias enanas, están ubicados dentro del cúmulo de galaxias Virgo relativamente cercano. Los cinco sistemas están separados de cualquier posible galaxia progenitora por más de 300.000 años luz en algunos casos, lo que dificulta la identificación de sus orígenes.
Los astrónomos encontraron los nuevos sistemas después de que otro grupo de investigación, dirigido por Elizabeth Adams del Instituto Holandés de Radioastronomía, compiló un catálogo de nubes de gas cercanas, proporcionando una lista de ubicaciones potenciales para nuevas galaxias. Después de que se publicó ese catálogo, varios grupos de investigación, incluido uno dirigido por el profesor asociado de astronomía de UArizona, David Sand, comenzaron a buscar estrellas que pudieran estar asociadas con estas nubes de gas.
Alguna vez se pensó que las nubes de gas estaban asociadas con nuestra propia galaxia, y la mayoría de ellas probablemente lo estén, pero cuando se descubrió la primera colección de estrellas, llamada SECCO1, los astrónomos se dieron cuenta de que no estaba cerca de la galaxia.[{» attribute=»»>Milky Way at all, but rather in the Virgo cluster, which is much farther away but still very nearby in the scale of the universe.
SECCO1 was one of the very unusual “blue blobs,” said Michael Jones, a postdoctoral fellow in the UArizona Steward Observatory and lead author of a study that describes the new stellar systems. Jones presented the findings, which Sand co-authored, during the 240th American Astronomical Society meeting in Pasadena, California, Wednesday.
“It’s a lesson in the unexpected,” Jones said. “When you’re looking for things, you’re not necessarily going to find the thing you’re looking for, but you might find something else very interesting.”
The team obtained their observations from the Hubble Space Telescope, the Very Large Array telescope in New Mexico and the Very Large Telescope in Chile. Study co-author Michele Bellazzini, with the Istituto Nazionale di Astrofisica in Italy, led the analysis of the data from Very Large Telescope and has submitted a companion paper focusing on that data.
“When a galaxy belly flops into a cluster that is full of hot gas, then its gas gets forced out behind it. That’s the mechanism that we think we’re seeing here to create these objects.”
Together, the team learned that most of the stars in each system are very blue and very young and that they contain very little atomic hydrogen gas. This is significant because star formation begins with atomic hydrogen gas, which eventually evolves into dense clouds of molecular hydrogen gas before forming into stars.
“We observed that most of the systems lack atomic gas, but that doesn’t mean there isn’t molecular gas,” Jones said. “In fact, there must be some molecular gas because they are still forming stars. The existence of mostly young stars and little gas signals that these systems must have lost their gas recently.”
The combination of blue stars and lack of gas was unexpected, as was a lack of older stars in the systems. Most galaxies have older stars, which astronomers refer to as being “red and dead.”
“Stars that are born red are lower mass and therefore live longer than blue stars, which burn fast and die young, so old red stars are usually the last ones left living,” Jones said. “And they’re dead because they don’t have any more gas with which to form new stars. These blue stars are like an oasis in the desert, basically.”
The fact that the new stellar systems are abundant in metals hints at how they might have formed.
“To astronomers, metals are any element heavier than helium,” Jones said. “This tells us that these stellar systems formed from gas that was stripped from a big galaxy, because how metals are built up is by many repeated episodes of star formation, and you only really get that in a big galaxy.”
There are two main ways gas can be stripped from a galaxy. The first is tidal stripping, which occurs when two big galaxies pass by each other and gravitationally tear away gas and stars.
The other is what’s known as ram pressure stripping.
“This is like if you belly flop into a swimming pool,” Jones said. “When a galaxy belly flops into a cluster that is full of hot gas, then its gas gets forced out behind it. That’s the mechanism that we think we’re seeing here to create these objects.”
The team prefers the ram pressure stripping explanation because in order for the blue blobs to have become as isolated as they are, they must have been moving very quickly, and the speed of tidal stripping is low compared to ram pressure stripping.
Astronomers expect that one day these systems will eventually split off into individual clusters of stars and spread out across the larger galaxy cluster.
What researchers have learned feeds into the larger “story of recycling of gas and stars in the universe,” Sand said. “We think that this belly-flopping process changes a lot of spiral galaxies into elliptical galaxies on some level, so learning more about the general process teaches us more about galaxy formation.”
Reference: “Young, blue, and isolated stellar systems in the Virgo Cluster. II. A new class of stellar system” by Michael G. Jones, David J. Sand, Michele Bellazzini, Kristine Spekkens, Ananthan Karunakaran, Elizabeth A. K. Adams, Giuseppina Battaglia, Giacomo Beccari, Paul Bennet, John M. Cannon, Giovanni Cresci, Denija Crnojevic, Nelson Caldwell, Jackson Fuson, Puragra Guhathakurta, Martha P. Haynes, John L. Inoue, Laura Magrini, Ricardo R. Munoz, Burcin Mutlu-Pakdil, Anil Seth, Jay Strader, Elisa Toloba and Dennis Zaritsky, 3 May 2022, Astrophysics > Astrophysics of Galaxies.
arXiv:2205.01695
