A new report from ESO (European Southern Observatory):
Cosmic Serpent ESO’s VLT captures details of an elaborate serpentine system sculpted by colliding stellar winds
The VISIR instrument on ESO’s Very Large Telescope has captured this stunning image of a newly discovered massive triple star system. Nicknamed Apep after an ancient Egyptian deity, this may be the first ever gamma-ray burst progenitor found.
The VISIR instrument on ESO’s VLT captured this stunning image of a newly-discovered massive binary star system. Nicknamed Apep after an ancient Egyptian deity, it could be the first gamma-ray burst progenitor to be found in our galaxy. Apep’s stellar winds have created the dust cloud surrounding the system, which consists of a binary star with a fainter companion. With 2 Wolf-Rayet stars orbiting each other in the binary, the serpentine swirls surrounding Apep are formed by the collision of two sets of powerful stellar winds, which create the spectacular dust plumes seen in the image. The reddish pinwheel in this image is data from the VISIR instrument on ESO’s Very Large Telescope (VLT), and shows the spectacular plumes of dust surrounding Apep. The blue sources at the centre of the image are a triple star system — which consists of a binary star system and a companion single star bound together by gravity. Though only two star-like objects are visible in the image, the lower source is in fact an unresolved binary Wolf-Rayet star. The triple star system was captured by the NACO adaptive optics instrument on the VLT. [Higher-res image files] This serpentine swirl, captured by the VISIR instrument on ESO’s Very Large Telescope (VLT), has an explosive future ahead of it; it is a Wolf-Rayet star system, and a likely source of one of the most energetic phenomena in the Universe — a long-duration gamma-ray burst (GRB).
“This is the first such system to be discovered in our own galaxy,” explains Joseph Callingham of the Netherlands Institute for Radio Astronomy (ASTRON), lead author of the study reporting this system. “We never expected to find such a system in our own backyard” [1].
The system, which comprises a nest of massive stars surrounded by a “pinwheel” of dust, is officially known only by unwieldy catalogue references like 2XMM J160050.7-514245. However, the astronomers chose to give this fascinating object a catchier moniker — “Apep”.
Apep got its nickname for its sinuous shape, reminiscent of a snake coiled around the central stars. Its namesake was an ancient Egyptian deity, a gargantuan serpent embodying chaos — fitting for such a violent system. It was believed that Ra, the Sun god, would battle with Apep every night; prayer and worship ensured Ra’s victory and the return of the Sun.
GRBs are among the most powerful explosions in the Universe. Lasting between a few thousandths of a second and a few hours, they can release as much energy as the Sun will output over its entire lifetime. Long-duration GRBs — those which last for longer than 2 seconds — are believed to be caused by the supernova explosions of rapidly-rotating Wolf-Rayet stars.
Some of the most massive stars evolve into Wolf-Rayet stars towards the end of their lives. This stage is short-lived, and Wolf-Rayets survive in this state for only a few hundred thousand years — the blink of an eye in cosmological terms. In that time, they throw out huge amounts of material in the form of a powerful stellar wind, hurling matter outwards at millions of kilometres per hour; Apep’s stellar winds were measured to travel at an astonishing 12 million km/h.
These stellar winds have created the elaborate plumes surrounding the triple star system — which consists of a binary star system and a companion single star bound together by gravity. Though only two star-like objects are visible in the image, the lower source is in fact an unresolved binary Wolf-Rayet star. This binary is responsible for sculpting the serpentine swirls surrounding Apep, which are formed in the wake of the colliding stellar winds from the two Wolf-Rayet stars.
Compared to the extraordinary speed of Apep’s winds, the dust pinwheel itself swirls outwards at a leisurely pace, “crawling” along at less than 2 million km/h. The wild discrepancy between the speed of Apep’s rapid stellar winds and that of the unhurried dust pinwheel is thought to result from one of the stars in the binary launching both a fast and a slow wind — in different directions.
This would imply that the star is undergoing near-critical rotation — that is, rotating so fast that it is nearly ripping itself apart. A Wolf-Rayet star with such rapid rotation is believed to produce a long-duration GRB when its core collapses at the end of its life.
The image is a colour composite made from exposures from the Digitized Sky Survey 2 (DSS2), and shows the region surrounding 2XMM J160050.7-514245, nicknamed “Apep”. The field of view is approximately 2.4 x 2.0 degrees. [Higher-res image files] Notes [1] Callingham, now at the Netherlands Institute for Radio Astronomy (ASTRON), did part of this research while at the University of Sydney working with research team leader Peter Tuthill. In addition to observations from ESO telescopes, the team also used the Anglo-Australian Telescope at Siding Spring Observatory, Australia.
The nearest single star to the Sun hosts an exoplanet at least 3.2 times as massive as Earth — a so-called super-Earth. Data from a worldwide array of telescopes, including ESO’s planet-hunting HARPS instrument, have revealed this frozen, dimly lit world. The newly discovered planet is the second-closest known exoplanet to the Earth and orbits the fastest moving star in the night sky. This image shows an artist’s impression of the planet’s surface. [Higher-res images]
The nearest single star to the Sun hosts an exoplanet at least 3.2 times as massive as Earth — a so-called super-Earth. One of the largest observing campaigns to date using data from a world-wide array of telescopes, including ESO’s planet-hunting HARPS instrument, have revealed this frozen, dimly lit world. The newly discovered planet is the second-closest known exoplanet to the Earth. Barnard’s star is the fastest moving star in the night sky.
The planet, designated Barnard’s Star b, now steps in as the second-closest known exoplanet to Earth [1]. The gathered data indicate that the planet could be a super-Earth, having a mass at least 3.2 times that of the Earth, which orbits its host star in roughly 233 days. Barnard’s Star, the planet’s host star, is a red dwarf, a cool, low-mass star, which only dimly illuminates this newly-discovered world. Light from Barnard’s Star provides its planet with only 2% of the energy the Earth receives from the Sun.
Despite being relatively close to its parent star — at a distance only 0.4 times that between Earth and the Sun — the exoplanet lies close to the snow line, the region where volatile compounds such as water can condense into solid ice. This freezing, shadowy world could have a temperature of –170 ℃, making it inhospitable for life as we know it.
Named for astronomer E. E. Barnard, Barnard’s Star is the closest single star to the Sun. While the star itself is ancient — probably twice the age of our Sun — and relatively inactive, it also has the fastest apparent motion of any star in the night sky [2]. Super-Earths are the most common type of planet to form around low-mass stars such as Barnard’s Star, lending credibility to this newly discovered planetary candidate. Furthermore, current theories of planetary formation predict that the snow line is the ideal location for such planets to form.
Previous searches for a planet around Barnard’s Star have had disappointing results — this recent breakthrough was possible only by combining measurements from several high-precision instruments mounted on telescopes all over the world [3].
“After a very careful analysis, we are 99% confident that the planet is there,” stated the team’s lead scientist, Ignasi Ribas (Institute of Space Studies of Catalonia and the Institute of Space Sciences, CSIC in Spain). “However, we’ll continue to observe this fast-moving star to exclude possible, but improbable, natural variations of the stellar brightness which could masquerade as a planet.”
Among the instruments used were ESO’s famous planet-hunting HARPS and UVES spectrographs.
“HARPS played a vital part in this project. We combined archival data from other teams with new, overlapping, measurements of Barnard’s star from different facilities,”
commented Guillem Anglada Escudé (Queen Mary University of London), co-lead scientist of the team behind this result [4].
“The combination of instruments was key to allowing us to cross-check our result.”
The astronomers used the Doppler effect to find the exoplanet candidate. While the planet orbits the star, its gravitational pull causes the star to wobble. When the star moves away from the Earth, its spectrum redshifts; that is, it moves towards longer wavelengths. Similarly, starlight is shifted towards shorter, bluer, wavelengths when the star moves towards Earth.
Astronomers take advantage of this effect to measure the changes in a star’s velocity due to an orbiting exoplanet — with astounding accuracy. HARPS can detect changes in the star’s velocity as small as 3.5 km/h — about walking pace. This approach to exoplanet hunting is known as the radial velocity method, and has never before been used to detect a similar super-Earth type exoplanet in such a large orbit around its star.
“We used observations from seven different instruments, spanning 20 years of measurements, making this one of the largest and most extensive datasets ever used for precise radial velocity studies.” explained Ribas. ”The combination of all data led to a total of 771 measurements — a huge amount of information!”
“We have all worked very hard on this breakthrough,” concluded Anglada-Escudé. “This discovery is the result of a large collaboration organised in the context of the Red Dots project, that included contributions from teams all over the world. Follow-up observations are already underway at different observatories worldwide.”
This wide-field image shows the surroundings of the red dwarf known as Barnard’s Star in the constellation of Ophiuchus (the Serpent-Bearer). This picture was created from material forming part of the Digitized Sky Survey 2. The centre of the image shows Barnard’s Star captured in three different exposures. The star is the fastest moving star in the night sky and its large apparent motion can be seen as its position changes between successive observations — shown in red, yellow and blue. [Higher-res images] Notes [1] The only stars closer to the Sun make up the triple star system Alpha Centauri. In 2016, astronomers using ESO telescopes and other facilities found clear evidence of a planet orbiting the closest star to Earth in this system, Proxima Centauri. That planet lies just over 4 light-years from Earth, and was discovered by a team led by Guillem Anglada Escudé.
[2] The total velocity of Barnard’s Star with respect to the Sun is about 500 000 km/h. Despite this blistering pace, it is not the fastest known star. What makes the star’s motion noteworthy is how fast it appears to move across the night sky as seen from the Earth, known as its apparent motion. Barnard’s Star travels a distance equivalent to the Moon’s diameter across the sky every 180 years — while this may not seem like much, it is by far the fastest apparent motion of any star.
Composite image of the Abell 2597 galaxy cluster showing the fountain-like flow of gas powered by the supermassive black hole in the central galaxy. The yellow is ALMA data showing cold gas. The red is data from the MUSE instrument on ESO’s Very Large Telescope showing the hot hydrogen gas in the same region. The blue-purple is the extended hot, ionized gas as imaged by the Chandra X-ray Observatory. The yellow ALMA data shows infalling material and the red MUSE data shows material launched in a vast spout by the black hole. [Hi-Res versions] Observations by ALMA and data from the MUSE spectrograph on ESO’s VLT have revealed a colossal fountain of molecular gas powered by a black hole in the brightest galaxy of the Abell 2597 cluster — the full galactic cycle of inflow and outflow powering this vast cosmic fountain has never before been observed in one system.
A mere one billion light-years away in the nearby galaxy cluster known as Abell 2597, there lies a gargantuan galactic fountain. A massive black hole at the heart of a distant galaxy has been observed pumping a vast spout of cold molecular gas into space, which then rains back onto the black hole as an intergalactic deluge. The in- and outflow of such a vast cosmic fountain has never before been observed in combination, and has its origin in the innermost 100 000 light-years of the brightest galaxy in the Abell 2597 cluster.
“This is possibly the first system in which we find clear evidence for both cold molecular gas inflow toward the black hole and outflow or uplift from the jets that the black hole launches,” explained Grant Tremblay of the Harvard-Smithsonian Center for Astrophysics and former ESO Fellow, who led this study. “The supermassive black hole at the centre of this giant galaxy acts like a mechanical pump in a fountain.”
Tremblay and his team used ALMA to track the position and motion of molecules of carbon monoxide within the nebula. These cold molecules, with temperatures as low as minus 250–260°C, were found to be falling inwards to the black hole. The team also used data from the MUSE instrument on ESO’s Very Large Telescope to track warmer gas — which is being launched out of the black hole in the form of jets.
“The unique aspect here is a very detailed coupled analysis of the source using data from ALMA and MUSE,” Tremblay explained. “The two facilities make for an incredibly powerful combination.”
Together these two sets of data form a complete picture of the process; cold gas falls towards the black hole, igniting the black hole and causing it to launch fast-moving jets of incandescent plasma into the void. These jets then spout from the black hole in a spectacular galactic fountain. With no hope of escaping the galaxy’s gravitational clutches, the plasma cools off, slows down, and eventually rains back down on the black hole, where the cycle begins anew.
This zoom video starts with a wide view of the Milky Way and ends with a close-up of the Abell 2597 cluster. Observations by ALMA and data from the MUSE spectrograph on ESO’s VLT have revealed a colossal fountain of molecular gas powered by a black hole in the brightest galaxy of the Abell 2597 cluster — the galactic cycle powering this vast cosmic fountain has never before been observed so clearly. The final shot is a composite image of the Abell 2597 galaxy cluster showing the fountain-like flow of gas powered by the supermassive black hole in the central galaxy. The yellow is ALMA data showing cold gas. The red is data from the MUSE instrument on ESO’s Very Large Telescope showing the hot hydrogen gas in the same region. The extend purple is the extended hot, ionized gas as imaged by the Chandra X-ray Observatory. Credit: ESO and Digitized Sky Survey 2, N. Risinger (skysurvey.org) Music: Astral Electronic.
This unprecedented observation could shed light on the life cycle of galaxies. The team speculates that this process may be not only common, but also essential to understanding galaxy formation. While the inflow and outflow of cold molecular gas have both previously been detected, this is the first time both have been detected within one system, and hence the first evidence that the two make up part of the same vast process.
In November, look for Pisces, Aries, and Triangulum in the night sky. Also be sure to catch the Taurid meteor shower, which features 5 to 10 meteors per hour on its peak night of November 5 to 6, and for meteors radiating from the constellation of Leo in the evening of November 17 and early morning of November 18.
ESO’s exquisitely sensitive GRAVITY instrument has added further evidence to the long-standing assumption that a supermassive black hole lurks in the centre of the Milky Way. New observations show clumps of gas swirling around at about 30% of the speed of light on a circular orbit just outside a four million solar mass black hole — the first time material has been observed orbiting close to the point of no return, and the most detailed observations yet of material orbiting this close to a black hole. This visualisation uses data from simulations of orbital motions of gas swirling around at about 30% of the speed of light on a circular orbit around the black hole. [Higher-res images] ESO’s exquisitely sensitive GRAVITY instrument has added further evidence to the long-standing assumption that a supermassive black hole lurks in the centre of the Milky Way. New observations show clumps of gas swirling around at about 30% of the speed of light on a circular orbit just outside its event horizon — the first time material has been observed orbiting close to the point of no return, and the most detailed observations yet of material orbiting this close to a black hole.
ESO’s GRAVITY instrument on the Very Large Telescope (VLT) Interferometer has been used by scientists from a consortium of European institutions, including ESO [1], to observe flares of infrared radiation coming from the accretion disc around Sagittarius A*, the massive object at the heart of the Milky Way. The observed flares provide long-awaited confirmation that the object in the centre of our galaxy is, as has long been assumed, a supermassive black hole. The flares originate from material orbiting very close to the black hole’s event horizon — making these the most detailed observations yet of material orbiting this close to a black hole.
This visible light wide-field view shows the rich star clouds in the constellation of Sagittarius (the Archer) in the direction of the centre of our Milky Way galaxy. The entire image is filled with vast numbers of stars — but far more remain hidden behind clouds of dust and are only revealed in infrared images. This view was created from photographs in red and blue light and forming part of the Digitized Sky Survey 2. The field of view is approximately 3.5 degrees x 3.6 degrees. [ Higher-res images]. While some matter in the accretion disc — the belt of gas orbiting Sagittarius A* at relativistic speeds [2] — can orbit the black hole safely, anything that gets too close is doomed to be pulled beyond the event horizon. The closest point to a black hole that material can orbit without being irresistibly drawn inwards by the immense mass is known as the innermost stable orbit, and it is from here that the observed flares originate.
“It’s mind-boggling to actually witness material orbiting a massive black hole at 30% of the speed of light,” marvelled Oliver Pfuhl, a scientist at the MPE. “GRAVITY’s tremendous sensitivity has allowed us to observe the accretion processes in real time in unprecedented detail.“
These measurements were only possible thanks to international collaboration and state-of-the-art instrumentation [3]. The GRAVITY instrument which made this work possible combines the light from four telescopes of ESO’s VLT to create a virtual super-telescope 130 metres in diameter, and has already been used to probe the nature of Sagittarius A*.
Earlier this year, GRAVITY and SINFONI, another instrument on the VLT, allowed the same team to accurately measure the close fly-by of the star S2 as it passed through the extreme gravitational field near Sagittarius A*, and for the first time revealed the effects predicted by Einstein’s general relativity in such an extreme environment. During S2’s close fly-by, strong infrared emission was also observed.
“We were closely monitoring S2, and of course we always keep an eye on Sagittarius A*,” explained Pfuhl. “During our observations, we were lucky enough to notice three bright flares from around the black hole — it was a lucky coincidence!“
This emission, from highly energetic electrons very close to the black hole, was visible as three prominent bright flares, and exactly matches theoretical predictions for hot spots orbiting close to a black hole of four million solar masses [4]. The flares are thought to originate from magnetic interactions in the very hot gas orbiting very close to Sagittarius A*.
The central parts of our Galaxy, the Milky Way, as observed in the near-infrared with the NACO instrument on ESO’s Very Large Telescope. By following the motions of the most central stars over more than 16 years, astronomers were able to determine the mass of the supermassive black hole that lurks there. [Higher-res images] Reinhard Genzel, of the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany, who led the study, explained:
“This always was one of our dream projects but we did not dare to hope that it would become possible so soon.” Referring to the long-standing assumption that Sagittarius A* is a supermassive black hole, Genzel concluded that “the result is a resounding confirmation of the massive black hole paradigm.“
[2] Relativistic speeds are those which are so great that the effects of Einstein’s Theory of Relativity become significant. In the case of the accretion disc around Sagittarius A*, the gas is moving at roughly 30% of the speed of light.
[3] GRAVITY was developed by a collaboration consisting of the Max Planck Institute for Extraterrestrial Physics (Germany), LESIA of Paris Observatory–PSL/CNRS/Sorbonne Université/Univ. Paris Diderot and IPAG of Université Grenoble Alpes/CNRS (France), the Max Planck Institute for Astronomy (Germany), the University of Cologne (Germany), the CENTRA–Centro de Astrofísica e Gravitação (Portugal) and ESO.
[4] The solar mass is a unit used in astronomy. It is equal to the mass of our closest star, the Sun, and has a value of 1.989 × 1030 kg. This means that Sgr A* has a mass 1.3 trillion times greater than the Earth.
