One of the fundamental questions in astronomy is how galaxies formed over 13 billion years ago and have evolved since then. A common feature that astronomers have noticed is that most galaxies seem to have supermassive black holes (SMBHs) in their center – like Sagittarius A*, solar mass ~4 million SMBH at the center of the Milky Way. These monstrous black holes sometimes swallow nearby gas, dust, and stars and emit excess energy in the form of powerful relativistic jets. This phenomenon, where the galactic center outshines the stars in the disk, is known as active galactic nucleus (AGN) or quasar.
In a recent study, an international team of astronomers led by European Southern Observatory (ESO) discovered a galaxy in the early universe that could reveal more about this evolution. using very large telescope (VLT) and Large Atacama Group Millimeter / Meter (ALMA) in Chile, they observed a swarm of galaxies orbiting a very bright galaxy and strongly forming stars in the early universe. These observations provide insight into how exceptionally bright galaxies grow and evolve into quasars, releasing powerful bursts of light through the visible universe.
The research was led by Michelle Ginolfi, Research Fellow at European Southern Observatory (ESO) in Garching, Germany. He was joined by researchers from National Institute of Astrophysics (INAF), and Cavendish LaboratoryThe Kavli Institute of CosmologyThe Max Planck Institute for Astrophysics (MPIA), and cosmic dawn center (dawn), and Niels Borg Institute (NBI), and Paris Institute of Astrophysics (IAP), and multiple universities. The paper describing their findings appeared recently in the journal Nature Connections.
Originally observed in 1963, quasars (short for quasars) were named because they resemble stars but shine in the radio spectrum. Today, the term is used to describe all supermassive black holes that are particularly luminous because of how they consume surrounding gas, dust, and stars. Today, many details about how galaxies transition from being “normal” to quasars are still unknown. To learn more about this process, Ginolfi and colleagues examined W0410-0913, one of the brightest, most massive and gas-rich galaxies observed in the early universe.
This galaxy is located about 12 billion light-years from Earth, and appears to astronomers as it was about a billion years after the Big Bang. What makes W0410-0913 so bright is how the dust is heated by the central black hole and the stars around it. This makes this type of galaxy appear particularly bright in the infrared spectrum, leading to the name “hot dust-shielded galaxies” (also known as “hot DOGs”). As Ginolfi explained recently press release From the Niels Bohr Institute:
Before evolving into a full-fledged quasar, some galaxies are thought to go through a very dusty and “active” phase in terms of star formation and gas accumulation on their central supermassive black holes. We set out to design an experiment to learn more about this transition.”
Since the evolution of galaxies is related to their surroundings, Ginolfi relied on the data he obtained multi-unit spectrophotometer (MUSE) in very large telescope (VLT) in Chile, which allowed them to study an area 40 times larger than the galaxy itself. They then consulted archival data obtained by the ALMA array, enabling them to measure the internal movement of gas within W0410-0913. As Peter Laursen, a researcher at the Cosmic Dawn Center in Copenhagen and co-author of the study, explained:
“Observations revealed that W0410-0913 is surrounded by a swarm of at least 24 smaller galaxies. The great thing about the MUSE instrument is that we can measure not only their position in the sky, but also their distance along our line of sight. In other words, we can measure their positions in 3D. “
This means that W0410-0913 resides in an area at least ten times denser than the normal universe. This was not entirely unexpected as hot dogs are supposed to live in dense environments. Moreover, W0410-0913 was 10 times larger than the size of our galaxy when the universe was about 1/8 the age of the current universe. Achieving this level of growth in such a short period of time, and feeding a supermassive black hole to achieve this level of brightness, would require a great deal of feed material.
This is consistent with well-established theories about how massive galaxies grow through accretion of gas and merge with satellite galaxies through gravity. In the dense environment occupied by W0410-0913, the research team predicted that it would undergo interactions and mergers with other galaxies at a very high rate. They also predicted that the inner part of the galaxy would be a chaotic swirl of clouds of gas and stars. In this regard, they were surprised when ALMA observations revealed that W0410-0913 did not appear to be at all disturbed by interactions with its neighbors.
In fact, ALMA observations showed that gas and stars orbited in an orderly fashion around the central black hole, even though they were moving at an incredible speed – at 500 kilometers per second (1.8 million km/h; 1.12 million mph)! Said Ginolfi:
“By coupling results from the two very different telescopes, we see a picture of how the most massive and dusty galaxies evolve. This type of galaxy, a vital stage in the transition from a dusty and star-forming galaxy to a quasar, tends to grow in very dense environments.. However, despite the expected frequent mergers with other galaxies, these gravitational interactions are not necessarily destructive – they feed the central galaxy and spin the gas a little, but leave it practically intact. It’s a bit like throwing small pebbles at a plate of hard glass: you can scratch it, but you won’t break it…“
These observations provide insight into how galaxies in the early universe evolved into what we see with the Milky Way’s neighbors today. It also provides the first clues regarding the processes driving the evolution of hot DOGs, an extreme and rare group of galaxies in our universe. From what Ginolfi and colleagues collected using VLT and ALMA, these galaxies grow in special, dense habitats but can still interact with their companions gently. In the coming years, there will be many opportunities to continue observing these and other early galaxies with next-generation telescopes.
This includes James Webb Space Telescope (JWST) The Caliph of Galilee Hubble – The Nancy Grace Roman Space Telescope (RST) – scheduled for launch in 2027. There are also next-generation ground-based telescopes that will join VLT and ALMA, including ESO very large telescope (ELT) and other 30m aperture tools, such as Giant Magellan Telescope (GMT) and Thirty meters telescope (TMT). Knowledge of the intricacies of how galaxies evolve is also expected to provide new insight into dark matter and dark energy and lead to more comprehensive models of cosmic evolution.