Astrônomos da Universidade do Arizona identificaram uma nova classe de sistema estelar. A coleção de estrelas azuis principalmente jovens é vista aqui usando a Câmera Avançada do Telescópio Espacial Hubble para Pesquisas. Crédito: Michael Jones
Acredita-se que as estruturas estelares sejam criadas quando as galáxias colidem com o gás quente em um processo que pode ser comparado a uma queda de barriga em uma piscina.
Astrônomos da Universidade do Arizona identificaram cinco exemplos de uma nova classe de sistema estelar. Eles não são exatamente galáxias e só existem isoladamente.
Os novos sistemas estelares contêm apenas estrelas jovens e azuis, que são distribuídas em um padrão irregular e parecem existir em surpreendente isolamento de qualquer galáxia-mãe em potencial.
Os sistemas estelares – que os astrônomos dizem que aparecem através de um telescópio como “bolhas azuis” e são do tamanho de pequenas galáxias anãs – estão localizados dentro do relativamente próximo aglomerado de galáxias de Virgem. Os cinco sistemas estão separados de quaisquer galáxias-mãe em potencial por mais de 300.000 anos-luz em alguns casos, tornando difícil identificar suas origens.
Os astrônomos encontraram os novos sistemas depois que outro grupo de pesquisa, liderado por Elizabeth Adams, do Instituto Holandês de Radioastronomia, compilou um catálogo de nuvens de gás próximas, fornecendo uma lista de locais potenciais de novas galáxias. Depois que esse catálogo foi publicado, vários grupos de pesquisa, incluindo um liderado pelo professor de astronomia associado da UArizona, David Sand, começaram a procurar estrelas que pudessem estar associadas a essas nuvens de gás.
Acreditava-se que as nuvens de gás estavam associadas à nossa própria galáxia, e a maioria delas provavelmente está, mas quando a primeira coleção de estrelas, chamada SECCO1, foi descoberta, os astrônomos perceberam que não estava perto da galáxia.[{” 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
Discussion about this post