The search for planets beyond our Solar System has grown immensely during the past few decades. To date, 4,521 extrasolar planets have been confirmed in 3,353 systems, with an additional 7,761 candidates awaiting confirmation. With so many distant worlds available for study (and improved instruments and methods), the process of exoplanet studies has been slowly transitioning away from discovery towards characterization.
For example, a team of international scientists recently showed how combining data from multiple observatories allowed them to reveal the structure and composition of an exoplanet’s upper atmosphere. The exoplanet in question is WASP-127b, a “hot Saturn” that orbits a Sun-like star located about 525 light-years away. These findings preview how astronomers will characterize exoplanet atmospheres and determine if they are conducive to life as we know it.
Located 63.4 light-years from Earth in the constellation Pictor is the young and bright blue star, Beta Pictoris. In 2008, observations conducted from the ESO’s Paranal Observatory in Chile confirmed the presence of an extrasolar planet. This planet was Beta Pictoris b, a Super-Jupiter with an orbital period of up between 6890 and 8890 days (~19 to 24 years) that was confirmed by directly imaging it as it passed behind the star.
In August of 2019, a second planet was detected (another Super-Jupiter) orbiting closer to Beta Pictoris. However, due to its proximity to its parent star, it could only be studied through indirect means (radial velocity measurements). After conducting a reanalysis of data obtained by the VLT, astronomers with the GRAVITY collaboration were able to confirm the existence of Beta Pictoris c through direct imaging.
About 370,000 years after the Big Bang, the Universe experienced a period that cosmologists refer to as the “Cosmic Dark Ages.” During this period, the Universe was obscured by pervasive neutral gas that obscured all visible light, making it invisible to astronomers. As the first stars and galaxies formed over the next few hundred millions of years, the radiation they emitted ionized this plasma, making the Universe transparent.
One of the biggest cosmological mysteries right now is when “cosmic reionization” began. To find out, astronomers have been looking deeper into the cosmos (and farther back in time) to spot the first visible galaxies. Thanks to new research by a team of astronomers from University College London (UCL), a luminous galaxy has been observed that was reionizing the intergalactic medium 13 billion years ago.
At the center of our galaxy, roughly 26,000 light-years from Earth, is the Supermassive Black Hole (SMBH) known as Sagittarius A*. The powerful gravity of this object and the dense cluster of stars around it provide astronomers with a unique environment for testing physics under the most extreme conditions. In particular, it offers them a chance to test Einstein’s Theory of General Relativity (GR).
For example, in the past thirty years, astronomers have been observing a star in the vicinity of Sagittarius A* (S2) to see if its orbit conforms to what is predicted by General Relativity. Recent observations made with the ESO’s Very Large Telescope (VLT) have completed an observation campaign that confirmed that the star’s orbit is rosette-shaped, once again proving that Einstein theory was right on the money!
Thanks to the latest generation of sophisticated telescopes, astronomers are learning things a great deal about our Universe. The improved resolution and observational power of these instruments also allow astronomers to address previously unanswered questions. Many of these telescopes can be found in the Atacama Desert in Chile, where atmospheric interference is minimal and the cosmos can be seen with greater clarity.
It is here that the European Southern Observatory (ESO) maintains many observatories, not the least of which is the Paranal Observatory where the Very Large Telescope (VLT) resides. Recently, an international team of astronomers used the VLT to study the center of the Milky Way and observed evidence of ancient starbursts. These indicate that the central region of our galaxy experienced an intense period of star birth in the past.
Fast-Radio Bursts (FRBs) are one of the most puzzling phenomena facing astronomers today. Essentially, FRBs are brief radio emissions from distant astronomical sources whose cause remains unknown. In some cases, FRBs that have been detected that have been repeating, but most have been one-off events. And while repeating sources have been tracked back to their point of origin, no single events have ever been localized.
Until now. Using the Australian Square Kilometer Array Pathfinder (ASKAP) and other radio telescopes from around the world, an Australian-led team of astronomers managed to confirm the distance to an intense radio burst that flashed for just a thousandth of a second. The constitutes the first non-repeating FRB to be traced back to its source, which in this case was a galaxy located 4 billion light-years away.
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.
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.
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:
In 2007, the European Southern Observatory (ESO) completed work on the Very Large Telescope (VLT) at the Paranal Observatory in northern Chile. This ground-based telescope is the world’s most advanced optical instrument, consisting of four Unit Telescopes with main mirrors (measuring 8.2 meters in diameter) and four movable 1.8-meter diameter Auxiliary Telescopes.
Recently, the VLT was upgraded with a new instrument known as the Multi Unit Spectroscopic Explorer (MUSE), a panoramic integral-field spectrograph that works at visible wavelengths. Thanks to the new adaptive optics mode that this allows for (known as laser tomography) the VLT was able to recently acquire some images of Neptune, star clusters and other astronomical objects with impeccable clarity.
In astronomy, adaptive optics refers to a technique where instruments are able to compensate for the blurring effect caused by Earth’s atmosphere, which is a serious issue when it comes to ground-based telescopes. Basically, as light passes through our atmosphere, it becomes distorted and causes distant objects to become blurred (which is why stars appear to twinkle when seen with the naked eye).
One solution to this problem is to deploy telescopes into space, where atmospheric disturbance is not an issue. Another is to rely on advanced technology that can artificially correct for the distortions, thus resulting in much clearer images. One such technology is the MUSE instrument, which works with an adaptive optics unit called a GALACSI – a subsystem of the Adaptive Optics Facility (AOF).
The instrument allows for two adaptive optics modes – the Wide Field Mode and the Narrow Field Mode. Whereas the former corrects for the effects of atmospheric turbulence up to one km above the telescope over a comparatively wide field of view, the Narrow Field mode uses laser tomography to correct for almost all of the atmospheric turbulence above the telescope to create much sharper images, but over a smaller region of the sky.
This consists of four lasers that are fixed to the fourth Unit Telescope (UT4) beaming intense orange light into the sky, simulating sodium atoms high in the atmosphere and creating artificial “Laser Guide Stars”. Light from these artificial stars is then used to determine the turbulence in the atmosphere and calculate corrections, which are then sent to the deformable secondary mirror of the UT4 to correct for the distorted light.
Using this Narrow Field Mode, the VLT was able to capture remarkably sharp test images of the planet Neptune, distant star clusters (such as the globular star cluster NGC 6388), and other objects. In so doing, the VLT demonstrated that its UT4 mirror is able to reach the theoretical limit of image sharpness and is no longer limited by the effects of atmospheric distortion.
This essentially means that it is now possible for the VLT to capture images from the ground that are sharper than those taken by the Hubble Space Telescope. The results from UT4 will also help engineers to make similar adaptations to the ESO’s Extremely Large Telescope (ELT), which will also rely on laser tomography to conduct its surveys and accomplish its scientific goals.
These goals include the study of supermassive black holes (SMBHs) at the centers of distant galaxies, jets from young stars, globular clusters, supernovae, the planets and moons of the Solar System, and extra-solar planets. In short, the use of adaptive optics – as tested and confirmed by the VLT’s MUSE – will allow astronomers to use ground-based telescopes to study the properties of astronomical objects in much greater detail than ever before.
In addition, other adaptive optics systems will benefit from work with the Adaptive Optics Facility (AOF) in the coming years. These include the ESO’s GRAAL, a ground layer adaptive optics module that is already being used by the Hawk-I infrared wide-field imager. In a few years, the powerful Enhanced Resolution Imager and Spectrograph (ERIS) instrument will also be added to the VLT.
Between these upgrades and the deployment of next-generation space telescopes in the coming years (like the James Webb Space Telescope, which will be deploying in 2021), astronomers expect to bringing a great deal more of the Universe “into focus”. And what they see is sure to help resolve some long-standing mysteries, and will probably create a whole lot more!
And be sure to enjoy these videos of the images obtained by the VLT of Neptune and NGC 6388, courtesy of the ESO:
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.
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.