Global climate change's effects will reach right up the skies, affecting such places as the VLTI in Chile. Courtesy ESO.
Alpha Centauri is the closest star system to us, at 4.37 light-years (about 25 trillion miles) away. In 2016, astronomers discovered an exoplanet orbiting one of the three stars in the Alpha Centauri system. Spurred on by that discovery, the European Southern Observatory (ESO) has developed a new instrument to find any other planets that might be in the Alpha Centauri system, and it’s busy looking right now.
The unique capabilities of the SPHERE instrument on ESO’s Very Large Telescope have enabled it to obtain the sharpest images of a double asteroid as it flew by Earth on 25 May. While this double asteroid was not itself a threatening object, scientists used the opportunity to rehearse the response to a hazardous Near-Earth Object (NEO), proving that ESO’s front-line technology could be critical in planetary defence. This artist’s impression shows both components of the double asteroid 1999 KW4 during its Earth fly-by.
On May 25th, 2019, a strange, double-asteroid (1999 KW4) flew past Earth at a distance and speed that is likely to make a lot of people nervous. As always, there was no danger, since the asteroid passed Earth at a minimum distance of 5.2 million km (3.23 million mi), over 15 times greater than the distance between Earth of the Moon, and its orbit is well-understood by scientists.
Because of this, flyby was the perfect opportunity for the International Asteroid Warning Network (IAWN) to conduct a cross-organizational observing campaign of the asteroid 1999 KW4 as it flew by Earth. The European Southern Observatory (ESO) took part in this campaign and managed to capture some images of the object using the Very Large Telescope (VLT).
2,000 light years away, in the Orion constellation, lurks an eerie looking creature, made of glowing gas lit up by young stars: the Cosmic Bat.
Its real name is NGC 1788. It’s a reflection nebula, meaning the light of nearby stars is strong enough to light it up, but not strong enough to ionize the gas, like in an emission nebula. Even though the stars are young and bright, the Cosmic Bat is still hidden. It took the powerful Very Large Telescope (VLT) to capture this image.
The Saturn nebula as imaged by the MUSE instrument on the ESO's Very Large Telescope. Image Credit: ESO/VLT
Saturn is an icon. There’s nothing else like it in the Solar System, and it’s something even children recognize. But there’s a distant object that astronomers call the Saturn nebula, because from a distance it resembles the planet, with its pronounced ringed shape.
The Saturn nebula bears no relation to the planet, except in shape. It’s about five thousand light years away, so in a small backyard telescope, it does resemble the planet. But when astronomers train large telescopes on it, the illusion falls apart.
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. Credit: ESO/Callingham et al.
When stars reach the end of their lifespan, many undergo gravitational collapse and explode into a supernova, In some cases, they collapse to become black holes and release a tremendous amount of energy in a short amount of time. These are what is known as gamma-ray bursts (GRBs), and they are one of the most powerful events in the known Universe.
Recently, an international team of astronomers was able to capture an image of a newly-discovered triple star system surrounded by a “pinwheel” of dust. This system, nicknamed “Apep”, is located roughly 8,000 light years from Earth and destined to become a long-duration GRB. In addition, it is the first of its kind to be discovered in our galaxy.
This image of the spiral galaxy NGC 3981 was captured by the FORS2 instrument on the ESO's VLT. NGC 3981 is in the Crater constellation. Image: ESO
The world’s most powerful telescopes have a lot of work to do. They’re tasked with helping us unravel the mysteries of the universe, like dark matter and dark energy. They’re burdened with helping us find other habitable worlds that might host life. And they’re busy with a multitude of other tasks, like documenting the end of a star’s life, or keeping an eye on meteors that get too close to Earth.
Artist’s impression of the path of the star S2 as it passes very close to the supermassive black hole at the centre of the Milky Way. Credit: ESO/M. Kornmesser
In 1915, Albert Einstein published his famous Theory of General Relativity, which provided a unified description of gravity as a geometric property of space and time. This theory gave rise to the modern theory of gravitation and revolutionized our understanding of physics. Even though a century has passed since then, scientists are still conducting experiments that confirm his theory’s predictions.
Thanks to recent observations made by a team of international astronomers (known as the GRAVITY collaboration), the effects of General Relativity have been revealed using a Supermassive Black Hole (SMBH) for the very first time. These findings were the culmination of a 26-year campaign of observations of the SMBH at the center of the Milky Way (Sagittarius A*) using the European Southern Observatory‘s (ESO) instruments.
Annotated image of the path of the star S2 as it passes very close to the supermassive black hole at the center of the Milky Way. Credit: ESO/M. Kornmesser
The new infrared observations collected by these instruments allowed the team to monitor one of the stars (S2) that orbits Sagittarius A* as it passed in front of the black hole – which took place in May of 2018. At the closest point in its orbit, the star was at a distance of less than 20 billion km (12.4 billion mi) from the black hole and was moving at a speed in excess of 25 million km/h (15 million mph) – almost three percent of the speed of light.
Whereas the SINFONI instrument was used to measure the velocity of S2 towards and away from Earth, the GRAVITY instrument in the VLT Interferometer (VLTI) made extraordinarily precise measurements of the changing position of S2 in order to define the shape of its orbit. The GRAVITY instrument then created the sharp images that revealed the motion of the star as it passed close to the black hole.
The team then compared the position and velocity measurements to previous observations of S2 using other instruments. They then compared these results with predictions made by Newton’s Law of Universal Gravitation, General Relativity, and other theories of gravity. As expected, the new results were consistent with the predictions made by Einstein over a century ago.
As Reinhard Genzel, who in addition to being the leader of the GRAVITY collaboration was a co-author on the paper, explained in a recent ESO press release:
“This is the second time that we have observed the close passage of S2 around the black hole in our galactic center. But this time, because of much improved instrumentation, we were able to observe the star with unprecedented resolution. We have been preparing intensely for this event over several years, as we wanted to make the most of this unique opportunity to observe general relativistic effects.”
When observed with the VLT’s new instruments, the team noted an effect called gravitational redshift, where the light coming from S2 changed color as it drew closer to the black hole. This was caused by the very strong gravitational field of the black hole, which stretched the wavelength of the star’s light, causing it to shift towards the red end of the spectrum.
The change in the wavelength of light from S2 agrees precisely with what Einstein’s field equation’s predicted. As Frank Eisenhauer – a researcher from the Max Planck Institute of Extraterrestrial Physics, the Principal Investigator of GRAVITY and the SINFONI spectrograph, and a co-author on the study – indicated:
“Our first observations of S2 with GRAVITY, about two years ago, already showed that we would have the ideal black hole laboratory. During the close passage, we could even detect the faint glow around the black hole on most of the images, which allowed us to precisely follow the star on its orbit, ultimately leading to the detection of the gravitational redshift in the spectrum of S2.”
Whereas other tests have been performed that have confirmed Einstein’s predictions, this is the first time that the effects of General Relativity have been observed in the motion of a star around a supermassive black hole. In this respect, Einstein has been proven right once again, using one the most extreme laboratory to date! What’s more, it confirmed that tests involving relativistic effects can provide consistent results over time and space.
“Here in the Solar System we can only test the laws of physics now and under certain circumstances,” said Françoise Delplancke, head of the System Engineering Department at ESO. “So it’s very important in astronomy to also check that those laws are still valid where the gravitational fields are very much stronger.”
In the near future, another relativistic test will be possible as S2 moves away from the black hole. This is known as a Schwarzschild precession, where the star is expected to experience a small rotation in its orbit. The GRAVITY Collaboration will be monitoring S2 to observe this effect as well, once again relying on the VLT’s very precise and sensitive instruments.
As Xavier Barcons (the ESO’s Director General) indicated, this accomplishment was made possible thanks to the spirit of international cooperation represented by the GRAVITY collaboration and the instruments they helped the ESO develop:
“ESO has worked with Reinhard Genzel and his team and collaborators in the ESO Member States for over a quarter of a century. It was a huge challenge to develop the uniquely powerful instruments needed to make these very delicate measurements and to deploy them at the VLT in Paranal. The discovery announced today is the very exciting result of a remarkable partnership.”
And be sure to check out this video of the GRAVITY Collaboration’s successful test, courtesy of the ESO:
This spectacular image from the SPHERE instrument on ESO's Very Large Telescope is the first clear image of a planet caught in the very act of formation around the dwarf star PDS 70. Credit: ESO/A. Müller et al.
For decades, the most widely-accepted view of how our Solar System formed has been the Nebular Hypothesis. According to this theory, the Sun, the planets, and all other objects in the Solar System formed from nebulous material billions of years ago. This dust experienced a gravitational collapse at the center, forming our Sun, while the rest of the material formed a circumstellar debris ring that coalesced to form the planets.
Thanks to the development of modern telescopes, astronomers have been able to probe other star systems to test this hypothesis. Unfortunately, in most cases, astronomers have only been able to observe debris rings around stars with hints of planets in formation. It was only recently that a team of European astronomers were able to capture an image of a newborn planet, thus demonstrating that debris rings are indeed the birthplace of planets.
Near infrared image of the PDS70 disk obtained with the SPHERE instrument. Credit: ESO/A. Müller, MPIA
For the sake of their studies, the teams selected PDS 70b, a planet that was discovered at a distance of 22 Astronomical Units (AUs) from its host star and which was believed to be a newly-formed body. In the first study – which was led by Miriam Keppler of the Max Planck Institute for Astronomy – the team indicated how they studied the protoplanetary disk around the star PDS 70.
Using these instruments, the team made the first robust detection of a young planet (PDS 70b) orbiting within a gap in its star’s protoplanetary disc and located roughly three billion km (1.86 billion mi) from its central star – roughly the same distance between Uranus and the Sun. In the second study, led by Andre Muller (also from the MPIA) the team describes how they used the SPHERE instrument to measure the brightness of the planet at different wavelengths.
From this, they were able to determine that PDS 70b is a gas giant that has about nine Jupiter masses and a surface temperature of about 1000 °C (1832 °F), making it a particularly “Hot Super-Jupiter”. The planet must be younger than its host star, and is probably still growing. The data also indicated that the planet is surrounded by clouds that alter the radiation emitted by the planetary core and its atmosphere.
Thanks to the advanced instruments used, the team was also able to acquire an image of the planet and its system. As you can see from the image (posted at top) and the video below, the planet is visible as a bright point to the right of the blackened center of the image. This dark region is due to a corongraph, which blocks the light from the star so the team could detect the much-fainter companion.
As Miriam Keppler, a postdoctoral student at the MPIA, explained in a recent ESO press statement:
“These discs around young stars are the birthplaces of planets, but so far only a handful of observations have detected hints of baby planets in them. The problem is that until now, most of these planet candidates could just have been features in the disc.”
In addition to spotting the young planet, the research teams also noted that it has sculpted the protoplanetary disc orbiting the star. Essentially, the planet’s orbit has traced a giant hole in the center of the disc after accumulating material from it. This means that PDS 70 b is still located in the vicinity of its birth place, is likely to still be accumulating material and will continue to grow and change.
For decades, astronomers have been aware of these gaps in the protoplanetary disc and speculated that they were produced by a planet. Now, they finally have the evidence to support this theory. As André Müller explained:
“Keppler’s results give us a new window onto the complex and poorly-understood early stages of planetary evolution. We needed to observe a planet in a young star’s disc to really understand the processes behind planet formation.“
These studies will be a boon to astronomers, especially when it comes to theoretical models of planet formation and evolution. By determining the planet’s atmospheric and physical properties, the astronomers have been able to test key aspects of the Nebular Hypothesis. The discovery of this young, dust-shrouded planet would not have been were if not for the capabilities of ESO’s SPHERE instrument.
This instrument studies exoplanets and discs around nearby stars using a technique known as high-contrast imaging, but also relies on advanced strategies and data processing techniques. In addition to blocking the light from a star with a coronagraph, SPHERE is able to filter out the signals of faint planetary companions around bright young stars at multiple wavelengths and epochs.
As Prof. Thomas Henning – the director at MPIA, the German co-investigator of the SPHERE instrument, and a senior author on the two studies – stated in a recent MPIA press release:
“After ten years of developing new powerful astronomical instruments such as SPHERE, this discovery shows us that we are finally able to find and study planets at the time of their formation. That is the fulfillment of a long-cherished dream.”
Future observations of this system will also allow astronomers to test other aspects of planet formation models and to learn about the early history of planetary systems. This data will also go a long way towards determining how our own Solar System formed and evolved during its early history.
This is just one of the spectacular images of dusky discs from the SPHERE instrument on ESO's Very Large Telescope. It shows the disc around the young star IM Lupi in finer detail than ever before. The collection of images shows the fascinating variety of shapes and sizes of discs. Image: ESO/H. Avenhaus et al./DARTT-S collaboration
The European Southern Observatory (ESO) has released a stunning collection of images of the circumstellar discs that surround young stars. The images were captured with the SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) instrument on the ESO’s Very Large Telescope (VLT) in Chile. We’ve been looking at images of circumstellar disks for quite some time, but this collection reveals the fascinating variety of shapes an sizes that these disks can take.
New images from the SPHERE instrument on ESO’s Very Large Telescope are revealing the dusty discs surrounding nearby young stars in greater detail than previously achieved. They show a bizarre variety of shapes, sizes and structures, including the likely effects of planets still in the process of forming. Image: ESO/H. Avenhaus et al./E. Sissa et al./DARTT-S and SHINE collaborations
We have a widely-accepted model of star formation supported by ample evidence, including images like these ones from the ESO. The model starts with a cloud of gas and dust called a giant molecular cloud. Within that cloud, a pocket of gas and dust begins to coalesce. Eventually, as gravity causes material to fall inward, the pocket becomes more massive, and exerts even more gravitational pull. More gas and dust continues to be drawn in.
The material that falls in also gives some angular momentum to the pocket, which causes rotation. Once enough material is accumulated, fusion ignites and a star is born. At that point, there is a proto-star inside the cloud, with unused gas and dust remaining in a rotating ring around the proto-star. That left over rotating ring is called a circumstellar disc, out of which planets eventually form.
There are other images of circumstellar discs, but they’ve been challenging to capture. To image any amount of detail in the disks requires blocking out the light of the star at the center of the disk. That’s where SPHERE comes in.
A detailed view of the SPHERE instrument and its main subsystems. SPHERE is installed on the ESO’s VLT and saw first light in 2014. Image: ESO
SPHERE was added to the ESO’s Very Large Telescope in 2014. It’s primary job is to directly image exoplanets, but it also has the ability to capture images of circumstellar discs. To do that, it separates two types of light: polarized, and non-polarized.
Light coming directly from a star—in these images, a young star still surrounded by a circumstellar disc—is non-polarized. But once that starlight is scattered by the material in the disk itself, the light becomes polarized. SPHERE, as its name suggests, is able to separate the two types of light and isolate just the light from the disk. That is how the instrument captures such fascinating images of the disks.
An edge-on view of the disc surrounding the star GSC 07396-00759. The disc extends from the lower-left to the upper-right and the central grey region shows where the star was masked out. Credit: ESO/E. Sissa et al.
Ever since it became clear that exoplanets are not rare, and that most stars—maybe all stars—have planets orbiting them, understanding solar system formation has become a hot topic. The problem has been that we can’t really see it happening in real time. We can look at our own Solar System, and other fully formed ones, and make guesses about how they formed. But planet formation is hidden inside those circumstellar disss. Seeing into those disks is crucial to understanding the link between the properties of the disk itself and the planets that form in the system.
The discs imaged in this collection are mostly from a study called the DARTTS-S (Discs ARound T Tauri Stars with SPHERE) survey. T Tauri stars are young stars less than 10 million years old. At that age, planets are still in the process of forming. The stars range from 230 to 550 light-years away from Earth. In astronomical terms, that’s pretty close. But the blinding bright light of the stars still makes it very difficult to capture the faint light of the discs.
One of the images is not a T Tauri star and is not from the DARTTS-S study. The disc around the star GSC 07396-00759, in the image above, is actually from the SHINE (SpHere INfrared survey for Exoplanets) survey, though the images itself was captured with SPHERE. GSC 07396-00759 is a red star that’s part of a multiple star system that was part of the DARTTS-S study. The puzzling thing is that red star is the same age as the T TAURI star in the same system, but the ring around the red star is much more evolved. Why the two discs around two stars the same age are so different from each other in terms of time-scale and evolution is a puzzle, and is one of the reasons why astronomers want to study these discs much more closely.
We can study our own Solar System, and look at the positions and characteristics of the planets and the asteroid belt and Kuiper Belt. From that we can try to guess how it all formed, but our only chance to understand how it all came together is to look at other younger solar systems as they form.
The SPHERE instrument, and other future instruments like the James Webb Space Telescope, will allow us to look into the circumstellar discs around other stars, and to tease out the details of planetary formation. These new images from SPHERE are a tantalizing taste of the detail and variety we can expect to see.
Artist's impression of the orbits of three of the stars very close to the supermassive black hole at the center of the Milky Way. Credit: ESO/M. Parsa/L. Calçada
At the center of our galaxy, roughly 26,000 light years from Earth, lies the Supermassive Black Hole (SMBH) known as Sagittarius A*. Measuring 44 million km across, this object is roughly 4 million times as massive as our Sun and exerts a tremendous gravitational pull. Since astronomers cannot detect black holes directly, its existence has been determined largely from the effect it has on the small group of stars orbiting it.
In this respect, scientists have found that observing Sagittarius A* is an effective way of testing the physics of gravity. For instance, in the course of observing these stars, a team of German and Czech astronomers noted subtle effects caused by the black hole’s gravity. In so doing, they were able to yet again confirm some of the predictions made by Einstein’s famous Theory of General Relativity.
Artist’s impression of part of S2s orbit around the supermassive black hole at the center of the Milky Way. Credit: ESO/M. Parsa/L. Calçada
From this, they measured the orbits of the stars that orbit Sagittarius A* to test predictions made by classical Newtonian physics (i.e. Universal Gravitation), as well as predictions based on general relativity. What they found was that one of the stars (S2) showed deviations in its orbit which were defied the former, but were consistent with the latter.
This star, which has 15 times the mass of our Sun, follows an elliptical orbit around the SMBH, completing a single orbit in about 15.6 years. At its closest, it gets to within 17 light hours of the black hole, which is the equivalent of 120 times the distance between the Sun and the Earth (120 AU). Essentially, the research team noted that S2 had the most elliptical orbit of any star orbiting the Supermassive Black Hole.
They also noted a slight change in its orbit – a few percent in the shape and about one-sixth of a degree in orientation. This could only be explained as being due to the relativistic effects caused by Sagittarius A* intense gravity, which cause a precession in its orbit. What this means is, the elliptical loop of S2’s orbit rotates around the SMBH over time, with its perihelion point aimed in different directions.
Interestingly enough, this is similar to the effect that was observed in Mercury’s orbit – aka. the “perihelion precession of Mercury” – during the late 19th century. This observation challenged classical Newtonian mechanics and led scientists to conclude that Newton’s theory of gravity was incomplete. It is also what prompted Einstein to develop his theory of General Relativity, which offered a satisfactory explanation for the issue.
Should the results of their study be confirmed, this will be the first time that the effects of general relativity have been precisely calculated using the stars that orbit a Supermassive Black Hole. Marzieh Parsa – a PhD student at the University of Cologne, Germany and lead author of the paper – was understandably excited with these results. As she stated in an ESO press statement:
“The Galactic Center really is the best laboratory to study the motion of stars in a relativistic environment. I was amazed how well we could apply the methods we developed with simulated stars to the high-precision data for the innermost high-velocity stars close to the supermassive black hole.“
This study was made possible thanks to the high-accuracy of the VLT’s instruments; in particular, the adaptive optics on the NACO camera and the SINFONI near-infrared spectrometer. These instruments were vital in tracking the star’s close approach and retreat from the black hole, which allowed for the team to precisely determine the shape of its orbit and thusly determine the relativistic effects on the star.
In addition to the more precise information about S2’s orbit, the team’s analysis also provided new and more accurate estimates of Sagittarius A* mass, as well as its distance from Earth. This could open up new avenues of research for this and other Supermassive Black Holes, as well as additional experiments that could help scientists to learn more about the physics of gravity.
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. Credit: ESO/MPE/S. Gillessen et al.
The results also provided a preview of the measurements and tests that will be taking place next year. In 2018, the star S2 will be making a very close approach to Sagittarius A*. Scientists from around the world will be using this opportunity to test the GRAVITY instrument, a second-generation instrument that was recently installed on the Very Large Telescope Interferometer (VLTI).
Developed by an international consortium led by the Max Planck Institute for Extraterrestrial Physics, this instrument has been conducting observations of the Galactic Center since 2016. In 2018, it will be used to measure the orbit of S2 with even greater precision, which is expected to be most revealing. At this time, astrophysicists will be seeking to make additional measurements of the SMBH’s general relativistic effects.
Beyond that, they also hope to detect additional deviations in the star’s orbit that could hint at the existence of new physics! With the right tools trained on the right place, and at the right time, scientists just might find that even Einstein’s theories of gravity were not entirely complete. But in the meantime, it looks like the late and great theoretical physicist was right again!
And be sure to check out this video of the recent study, courtesy of the ESO:
