Black hole caught zapping galaxy into existence?

These astronomers believe they have identified black hole jets as a possible driver of the formation of galaxies in the early universe.

The image above shows an artist’s impression of how jets from supermassive black holes could form galaxies. It illustrates a recent set of observations from the European Southern Observatory, which – according to the astronomers who conducted these observations – suggest that black holes may be “building” their own host galaxies.

“The ‘chicken and egg’ question of whether a galaxy or its black hole comes first is one of the most debated subjects in astrophysics today,” according to astronomer David Elbaz. “Our study suggests that supermassive black holes can trigger the formation of stars, thus ‘building’ their own host galaxies. This link could also explain why galaxies hosting larger black holes have more stars.”

To reach this conclusion, which this team of astronomers is calling “extraordinary,” they conducted extensive observations of a peculiar object, called HE0450-2958. This object is classified as a quasar. It is considered to be relatively nearby at some 5 billion light-years away. In 2005, astronomers announced that HE0450-2958 is “a quasar without a home,” in other words, a quasar without a home galaxy surrounding it. This is unusual because quasars are thought to be an early stage in galaxy evolution. In recent years, astronomers have agreed that quasars are compact regions surrounding central supermassive black holes residing in young galaxies in the early universe. The quasars are thought to be powered by energetic phenomena related to black hole accretion disks.

Until now, it was speculated that the host galaxy of HE0450-2958 was hidden behind large amounts of dust, and so the astronomers used an instrument on ESO’s Very Large Telescope (VLT) for the observations that detects radiation in the mid-infrared. At such wavelengths, dust clouds that cannot be seen with the eye shine very brightly. “Observing at these wavelengths would allow us to trace dust that might hide the host galaxy,” says Knud Jahnke, who led the observations. “However, we did not find any. Instead we discovered that an apparently unrelated galaxy in the quasar’s immediate neighborhood is producing stars at a frantic rate.”

These observations have provided a surprising new take on the system, according to these astronomers. While no trace of stars is revealed around the black hole, its companion galaxy is extremely rich in bright and very young stars. It is forming stars at a rate equivalent to about 350 suns per year, one hundred times more than rates for typical galaxies in the local universe.

Earlier observations had shown that the companion galaxy is, in fact, under fire: the quasar is spewing a jet of highly energetic particles towards its companion, accompanied by a stream of fast-moving gas. The injection of matter and energy into the galaxy indicates that the quasar itself might be inducing the formation of stars and thereby creating its own host galaxy. In such a scenario, galaxies would have evolved from clouds of gas hit by the energetic jets emerging from quasars, these astronomers say.

“The two objects are bound to merge in the future: the quasar is moving at a speed of only a few tens of thousands of km/h with respect to the companion galaxy and their separation is only about 22,000 light-years,” says Elbaz. “Although the quasar is still ‘naked’, it will eventually be ‘dressed’ when it merges with its star-rich companion. It will then finally reside inside a host galaxy like all other quasars.”

Hence, the team believes it has identified black hole jets as a possible driver of galaxy formation, which may also represent the long-sought missing link to understanding why the mass of black holes is larger in galaxies that contain more stars.

For more about these ideas – plus images and a video – go to
https://www.eso.org/public/outreach/press-rel/pr-2009/pr-46-09.html

Deborah Byrd