Stellar explosions are most often associated with supernovae, the spectacular deaths of stars. But new ALMA observations provide insights into explosions at the other end of the stellar life cycle, star birth. Astronomers captured these dramatic images as they explored the firework-like debris from the birth of a group of massive stars, demonstrating that star formation can be a violent and explosive process too.
Stellar explosions are most often associated with supernovae, the spectacular deaths of stars. But new ALMA observations of the Orion Nebula complex provide insights into explosions at the other end of the stellar life cycle, star birth. Astronomers captured these dramatic images of the remains of a 500-year-old explosion as they explored the firework-like debris from the birth of a group of massive stars, demonstrating that star formation can be a violent and explosive process too. The background image includes optical and near-infrared imaging from both the Gemini South and ESO Very Large Telescope. The famous Trapezium Cluster of hot young stars appears towards the bottom of this image. The ALMA data do not cover the full image shown here. [Larger images.]1350 light years away, in the constellation of Orion (the Hunter), lies a dense and active star formation factory called the Orion Molecular Cloud 1 (OMC-1), part of the same complex as the famous Orion Nebula. Stars are born when a cloud of gas hundreds of times more massive than our Sun begins to collapse under its own gravity. In the densest regions, protostars ignite and begin to drift about randomly. Over time, some stars begin to fall toward a common centre of gravity, which is usually dominated by a particularly large protostar — and if the stars have a close encounter before they can escape their stellar nursery, violent interactions can occur.
Stellar explosions are most often associated with supernovae, the spectacular deaths of stars. But new ALMA observations of the Orion Nebula complex provide insights into explosions at the other end of the stellar life cycle, star birth. This ESOcast Light takes a quick look at the important facts.
About 100 000 years ago, several protostars started to form deep within the OMC-1. Gravity began to pull them together with ever-increasing speed, until 500 years ago two of them finally clashed. Astronomers are not sure whether they merely grazed each other or collided head-on, but either way it triggered a powerful eruption that launched other nearby protostars and hundreds of colossal streamers of gas and dust out into interstellar space at over 150 kilometres per second. This cataclysmic interaction released as much energy as our Sun emits in 10 million years.
Stellar explosions are most often associated with supernovae, the spectacular deaths of stars. But new ALMA observations of the Orion Nebula complex provide insights into explosions at the other end of the stellar life cycle, star birth. Astronomers captured these dramatic images of the remains of a 500-year-old explosion as they explored the firework-like debris from the birth of a group of massive stars, demonstrating that star formation can be a violent and explosive process too. The background is an infrared image from the HAWK-I camera on ESO’s Very Large Telescope. The ALMA data only cover the region marked by the box. [Larger images.]Fast forward 500 years, and a team of astronomers led by John Bally (University of Colorado, USA) has used the Atacama Large Millimeter/submillimeter Array (ALMA) to peer into the heart of this cloud. There they found the flung-out debris from the explosive birth of this clump of massive stars, looking like a cosmic version of fireworks with giant streamers rocketing off in all directions.
This video takes the viewer deep into the famous constellation of Orion (The Hunter). Hidden behind the glowing gas, dark dust and bright young stars of the Orion Nebula complex lies a strange object — the remains of a 500 year old interaction of recently formed stars. A new image from ALMA, which reveals this feature more clearly than ever before, is shown at the end of the sequence. Credit: ALMA (ESO/NAOJ/NRAO), J. Bally/H. Drass et al./N. Risinger (skysurvey.org). Music: Johan B. Monell
Such explosions are expected to be relatively short-lived, the remnants like those seen by ALMA lasting only centuries. But although they are fleeting, such protostellar explosions may be relatively common. By destroying their parent cloud, these events might also help to regulate the pace of star formation in such giant molecular clouds.
Hints of the explosive nature of the debris in OMC-1 were first revealed by the Submillimeter Array in Hawaii in 2009. Bally and his team also observed this object in the near-infrared with the Gemini South telescope in Chile, revealing the remarkable structure of the streamers, which extend nearly a light-year from end to end.
The new ALMA images, however, showcase the explosive nature in high resolution, unveiling important details about the distribution and high-velocity motion of the carbon monoxide (CO) gas inside the streamers. This will help astronomers understand the underlying force of the blast, and what impact such events could have on star formation across the galaxy.
This video sequence compares a new ALMA image of an explosive event in the Orion star forming region with an image taken in infrared light using the HAWK-I camera on ESO’s Very Large Telescope. Credit: ALMA (ESO/NAOJ/NRAO)/J. Bally/H. Drass et al. Music: Johan B. Monell
Artist’s impression of a galaxy forming stars within powerful outflows of material blasted out from supermassive black holes at its core. Results from ESO’s Very Large Telescope are the first confirmed observations of stars forming in this kind of extreme environment. The discovery has many consequences for understanding galaxy properties and evolution. [Larger images]Observations using ESO’s Very Large Telescope have revealed stars forming within powerful outflows of material blasted out from supermassive black holes at the cores of galaxies. These are the first confirmed observations of stars forming in this kind of extreme environment. The discovery has many consequences for understanding galaxy properties and evolution. The results are published in the journal Nature.
New observations from ESO’s Very Large Telescope have revealed stars forming in the huge outflows in galaxies, which are driven by central supermassive black holes. This ESOcast Light takes a quick look at the important facts. Credit: ESO
A UK-led group of European astronomers used the MUSE and X-shooter instruments on the Very Large Telescope (VLT) at ESO’s Paranal Observatory in Chile to study an ongoing collision between two galaxies, known collectively as IRAS F23128-5919, that lie around 600 million light-years from Earth. The group observed the colossal winds of material — or outflows — that originate near the supermassive black hole at the heart of the pair’s southern galaxy, and have found the first clear evidence that stars are being born within them [1].
Such galactic outflows are driven by the huge energy output from the active and turbulent centres of galaxies. Supermassive black holes lurk in the cores of most galaxies, and when they gobble up matter they also heat the surrounding gas and expel it from the host galaxy in powerful, dense winds [2].
“Astronomers have thought for a while that conditions within these outflows could be right for star formation, but no one has seen it actually happening as it’s a very difficult observation,”
comments team leader Roberto Maiolino from the University of Cambridge.
“Our results are exciting because they show unambiguously that stars are being created inside these outflows.”
The group set out to study stars in the outflow directly, as well as the gas that surrounds them. By using two of the world-leading VLT spectroscopic instruments, MUSE and X-shooter, they could carry out a very detailed study of the properties of the emitted light to determine its source.
Artist’s impression of a galaxy forming stars within powerful outflows of material blasted out from supermassive black holes at its core. Results from ESO’s Very Large Telescope are the first confirmed observations of stars forming in this kind of extreme environment. The discovery has many consequences for understanding galaxy properties and evolution. Credit: ESO/M. Kornmesser
Radiation from young stars is known to cause nearby gas clouds to glow in a particular way. The extreme sensitivity of X-shooter allowed the team to rule out other possible causes of this illumination, including gas shocks or the active nucleus of the galaxy.
The group then made an unmistakable direct detection of an infant stellar population in the outflow [3]. These stars are thought to be less than a few tens of millions of years old, and preliminary analysis suggests that they are hotter and brighter than stars formed in less extreme environments such as the galactic disc.
As further evidence, the astronomers also determined the motion and velocity of these stars. The light from most of the region’s stars indicates that they are travelling at very large velocities away from the galaxy centre — as would make sense for objects caught in a stream of fast-moving material.
Co-author Helen Russell (Institute of Astronomy, Cambridge, UK) expands:
“The stars that form in the wind close to the galaxy centre might slow down and even start heading back inwards, but the stars that form further out in the flow experience less deceleration and can even fly off out of the galaxy altogether.”
The discovery provides new and exciting information that could better our understanding of some astrophysics, including how certain galaxies obtain their shapes [4]; how intergalactic space becomes enriched with heavy elements[5]; and even from where unexplained cosmic infrared background radiation may arise [6].
Maiolino is excited for the future:
“If star formation is really occurring in most galactic outflows, as some theories predict, then this would provide a completely new scenario for our understanding of galaxy evolution.”
Notes
[1] Stars are forming in the outflows at a very rapid rate; the astronomers say that stars totalling around 30 times the mass of the Sun are being created every year. This accounts for over a quarter of the total star formation in the entire merging galaxy system.
[2] The expulsion of gas through galactic outflows leads to a gas-poor environment within the galaxy, which could be why some galaxies cease forming new stars as they age. Although these outflows are most likely to be driven by massive central black holes, it is also possible that the winds are powered by supernovae in a starburst nucleus undergoing vigorous star formation.
[3] This was achieved through the detection of signatures characteristic of young stellar populations and with a velocity pattern consistent with that expected from stars formed at high velocity in the outflow.
[4] Spiral galaxies have an obvious disc structure, with a distended bulge of stars in the centre and surrounded by a diffuse cloud of stars called a halo. Elliptical galaxies are composed mostly of these spheroidal components. Outflow stars that are ejected from the main disc could give rise to these galactic features.
[5] How the space between galaxies — the intergalactic medium — becomes enriched with heavy elements is still an open issue, but outflow stars could provide an answer. If they are jettisoned out of the galaxy and then explode as supernovae, the heavy elements they contain could be released into this medium.
[6] Cosmic-infrared background radiation, similar to the more famous cosmic microwave background, is a faint glow in the infrared part of the spectrum that appears to come from all directions in space. Its origin in the near-infrared bands, however, has never been satisfactorily ascertained. A population of outflow stars shot out into intergalactic space may contribute to this light.
The Alpha Centauri star system is ideal to search for habitable planets by various observing techniques due to its proximity and wide range of stellar masses. Following the recent discovery of an Earth-size planet candidate located inside the Proxima Centauri habitable zone, Dr. Marois will discuss this remarkable discovery and the planet’s potential to find life. He will also present our current instrument project for the Gemini South observatory, TIKI, to discover similar planets around the two Sun-like pair located 15,000 AU from Proxima Centauri. The Alpha Centauri system is the prime target of the Breakthrough Starshot program, a project to send small quarter-size probes to take resolve images of these new worlds, and to prepare for Humanity’s first step into a new star system.
More about Dr. Marois:
Dr Marois completed his Ph.D. at the Université de Montréal in 2004. The main topic of his thesis work was to understand the limits in exoplanet imaging and to design innovating observing strategies. After his thesis, he did postdoctoral researches at the Lawrence Livermore National Laboratory, Univ. of California Berkeley and NRC. In 2008, while at NRC, he led the team that took the first image of another planetary system (HR 8799) using the Keck and Gemini telescopes. He is currently pursuing his research at the NRC Herzberg where he is part of the Gemini Planet Imager campaign, and leading the development of instruments for imaging Earth-like planets at Gemini South and at the TMT.
This composite image of the Kleinmann-Low Nebula, part of the Orion Nebula complex, is composed of several pointings of the NASA/ESA Hubble Space Telescope in optical and near-infrared light. Infrared light allows to peer through the dust of the nebula and to see the stars therein. The revealed stars are shown with a bright red colour in the image. With this image, showing the central region of the Orion Nebula, scientists were looking for rogue planets and brown dwarfs. As side-effect they found a fast-moving runaway star. [Larger image]In the search for rogue planets and failed stars astronomers using the NASA/ESA Hubble Space Telescope have created a new mosaic image of the Orion Nebula. During their survey of the famous star formation region, they found what may be the missing piece of a cosmic puzzle; the third, long-lost member of a star system that had broken apart.
The Orion Nebula is the closest star formation region to Earth, only 1400 light-years away. It is a turbulent place — stars are being born, planetary systems are forming and the radiation unleashed by young massive stars is carving cavities in the nebula and disrupting the growth of smaller, nearby stars.
This video starts with a ground-based image of the night sky, taken by Akira Fujii, zooms on the star formation region of the Orion Nebula — observed by Martin Kornmesser — and ends with a detailed view of the nebula as seen by Hubble. Credit: ESA/Hubble, A. Fujii, M. KornmesserMusic: Johan B. Monell (www.johanmonell.com)
Because of this ongoing turmoil, Hubble has observed the nebula many times to study the various intriguing processes going on there. This large composite image of the nebula’s central region, combining visual and near-infrared data, is the latest addition to this collection.
Astronomers used these new infrared data to hunt for rogue planets — free-floating in space without a parent star — and brown dwarfs in the Orion Nebula. The infrared capabilities of Hubble also allow it to peer through the swirling clouds of dust and gas and make the stars hidden within clearly visible; the unveiled stars appear with bright red colours in the final image. Among these, astronomers stumbled across a star moving at an unusually high speed — about 200 000 kilometres per hour [1]. This star could be the missing piece of the puzzle of a star system that had been broken apart 540 years ago.
This ground-based image was taken by Japanese amateur astronomer Akira Fujii and shows the constellations Orion, Canis Minor and Canis major. [Larger image]Astronomers already knew about two other runaway stars in the Orion Nebula which were most likely once part of a now-defunct multiple-star system. For years it was suspected that the original system contained more than just these two stars. Now, by virtue of accident and curiosity, Hubble may have found the missing third piece of this cosmic puzzle.
Whether the new star is indeed the missing — and the last — piece of the puzzle will require further observations. So will the answer to the question of why the original star system broke apart in the first place. While there are several theories — interactions with other, nearby stellar groups, or two of the stars getting too close to each other — none can be ruled out or confirmed yet.
And while the astronomers are looking for the answers to these questions, who knows what mystery they will find next?
Notes
[1] The relative speed of the star was calculated by comparing observations made in 1998 with the recent ones. The speed of the newly discovered star is almost 30 times the speed of most of the nebula’s stellar inhabitants.
