Using the microlensing metthod, a team of astrophysicists have found the first extra-galactic planets! Credit: NASA/Tim Pyle
In 2025, NASA’s next-generation telescope, the Wide-Field Infrared Survey Telescope (WFIRST), will take to space and join in the search for extrasolar planets. Between its 2.4-meter (8 ft) telescope, 18 detectors, 300-megapixel camera, and the extraordinary survey speed it will offer, the WFIRST will be able to scan areas of the sky a hundred times greater than the Hubble Space Telescope.
Beyond its high-sensitivity and advanced suite of instruments, WFIRST will also rely on a technique known as Gravitational Microlensing to search for and characterize exoplanets. This is essentially a small-scale version of the gravitational lensing technique, where the gravitational force of a massive object between the observer and the target is used to focus and magnify the light coming from a distant source.
Using the gravitational lensing technique, a team was able to examine how light from distant quasar was affected by intervening small clumps of dark matter. Credit: NASA/ESA/D. Player (STScI)
To put it simply, Dark Matter is not only believed to make up the bulk of the Universe’s mass but also acts as the scaffolding on which galaxies are built. But to find evidence of this mysterious, invisible mass, scientists are forced to rely on indirect methods similar to the ones used to study black holes. Essentially, they measure how the presence of Dark Matter affects stars and galaxies in its vicinity.
To date, astronomers have managed to find evidence of dark matter clumps around medium and large galaxies. Using data from the Hubble Space Telescope and a new observing technique, a team of astronomers from UCLA and NASA JPL found that dark matter can form much smaller clumps than previously thought. These findings were presented this week at the 235th meeting of the American Astronomical Society (AAS).
In this artist's conception, a rogue planet drifts through space. Credit: Christine Pulliam (CfA)
A team of researchers at the University of Oklahoma have discovered “planetary mass bodies” outside of the Milky Way. They were discovered in one gravitationally-lensed galaxy, and in one gravitationally-lensed galaxy cluster using a technique called quasar micro-lensing. According to the researchers, the planetary mass objects are either planets or primordial black holes.
One of the Daya Bay detectors.
Roy Kaltschmidt, Lawrence Berkeley National Laboratory
In 1960, famed theoretical physicist Freeman Dyson made a radical proposal. In a paper titled “Search for Artificial Stellar Sources of Infrared Radiation” he suggested that advanced extra-terrestrial intelligences (ETIs) could be found by looking for signs of artificial structures so large, they encompassed entire star systems (aka. megastructures). Since then, many scientists have come up with their own ideas for possible megastructures.
Like Dyson’s proposed Sphere, these ideas were suggested as a way of giving scientists engaged in the Search for Extra-Terrestrial Intelligence (SETI) something to look for. Adding to this fascinating field, Dr. Albert Jackson of the Houston-based technology company Triton Systems recently released a study where he proposed how an advanced ETI could use rely on a neutron star or black hole to focus neutrino beams to create a beacon.
The early universe. Credit: Tom Abel & Ralf Kaehler (KIPACSLAC)/ AMNH/NASA
For over fifty years, scientists have theorized that roughly 85% of matter in the Universe’s is made up of a mysterious, invisible mass. Since then, multiple observation campaigns have indirectly witnessed the effects that this “Dark Matter” has on the Universe. Unfortunately, all attempts to detect it so far have failed, leading scientists to propose some very interesting theories about its nature.
One such theory was offered by the late and great Stephen Hawking, who proposed that the majority of dark matter may actually be primordial black holes (PBH) smaller than a tenth of a millimeter in diameter. But after putting this theory through its most rigorous test to date, an international team of scientists led from the Kavli Institute for the Physics and Mathematics of the Universe (IPMU) has confirmed that it is not.
A Hubble Space Telescope image of a doubly-imaged quasar. Image Credit: NASA Hubble Space Telescope, Tommaso Treu/UCLA, and Birrer et al
How fast is the Universe expanding? That’s a question that astronomers haven’t been able to answer accurately. They have a name for the expansion rate of the Universe: The Hubble Constant, or Hubble’s Law. But measurements keep coming up with different values, and astronomers have been debating back and forth on this issue for decades.
The basic idea behind measuring the Hubble Constant is to look at distant light sources, usually a type of supernovae or variable stars referred to as ‘standard candles,’ and to measure the red-shift of their light. But no matter how astronomers do it, they can’t come up with an agreed upon value, only a range of values. A new study involving quasars and gravitational lensing might help settle the issue.
A supernova (bright spot at lower left) and its host galaxy (upper center), as they would appear if gravitationally lensed by an intervening black hole (center). Credit: Miguel Zumalacárregui/UC Berkeley
In February of 2016, scientists working for the Laser Interferometer Gravitational-Wave Observatory (LIGO) made history when they announced the first-ever detection of gravitational waves. Since that time, multiple detections have taken place and scientific collaborations between observatories – like Advanced LIGO and Advanced Virgo – are allowing for unprecedented levels of sensitivity and data sharing.
This event not only confirmed a century-old prediction made by Einstein’s Theory of General Relativity, it also led to a revolution in astronomy. It also stoked the hopes of some scientists who believed that black holes could account for the Universe’s “missing mass”. Unfortunately, a new study by a team of UC Berkeley physicists has shown that black holes are not the long-sought-after source of Dark Matter.
Hubble image of a luminous red galaxy (LRG) gravitationally distorting the light from a much more distant blue galaxy, a technique known as gravitational lensing. The shape of the galaxy doing the lensing created an almost circular image. An oblong galaxy would create more of an Einstein Ring effect. Credit: ESA/Hubble & NASA
When looking to study the most distant objects in the Universe, astronomers often rely on a technique known as Gravitational Lensing. Based on the principles of Einstein’s Theory of General Relativity, this technique involves relying on a large distribution of matter (such as a galaxy cluster or star) to magnify the light coming from a distant object, thereby making it appear brighter and larger.
This technique has allowed for the study of individual stars in distant galaxies. In a recent study, an international team of astronomers used a galaxy cluster to study the farthest individual star ever seen in the Universe. Although it normally to faint to observe, the presence of a foreground galaxy cluster allowed the team to study the star in order to test a theory about dark matter.
For the sake of their study, Prof. Kelly and his associates used the galaxy cluster known as MACS J1149+2223 as their lens. Located about 5 billion light-years from Earth, this galaxy cluster sits between the Solar System and the galaxy that contains Icarus. By combining Hubble’s resolution and sensitivity with the strength of this gravitational lens, the team was able to see and study Icarus, a blue giant.
Icarus, named after the Greek mythological figure who flew too close to the Sun, has had a rather interesting history. At a distance of roughly 9 billion light-years from Earth, the star appears to us as it did when the Universe was just 4.4 billion years old. In April of 2016, the star temporarily brightened to 2,000 times its normal luminosity thanks to the gravitational amplification of a star in MACS J1149+2223.
As Prof. Kelly explained in a recent UCLA press release, this temporarily allowed Icarus to become visible for the first time to astronomers:
“You can see individual galaxies out there, but this star is at least 100 times farther away than the next individual star we can study, except for supernova explosions.”
Kelly and a team of astronomers had been using Hubble and MACS J1149+2223 to magnify and monitor a supernova in the distant spiral galaxy at the time when they spotted the new point of light not far away. Given the position of the new source, they determined that it should be much more highly magnified than the supernova. What’s more, previous studies of this galaxy had not shown the light source, indicating that it was being lensed.
Icarus, the farthest individual star ever seen, shown at left. Panels at right show the view in 2011, without Icarus visible, compared with the star’s brightening in 2016. Credit: NASA, ESA and Patrick Kelly/University of Minnesota
As Tommaso Treu, a professor of physics and astronomy in the UCLA College and a co-author of the study, indicated:
“The star is so compact that it acts as a pinhole and provides a very sharp beam of light. The beam shines through the foreground cluster of galaxies, acting as a cosmic magnifying glass… Finding more such events is very important to make progress in our understanding of the fundamental composition of the universe.
In this case, the star’s light provided a unique opportunity to test a theory about the invisible mass (aka. “dark matter”) that permeates the Universe. Basically, the team used the pinpoint light source provided by the background star to probe the intervening galaxy cluster and see if it contained huge numbers of primordial black holes, which are considered to be a potential candidate for dark matter.
These black holes are believed to have formed during the birth of the Universe and have masses tens of times larger than the Sun. However, the results of this test showed that light fluctuations from the background star, which had been monitored by Hubble for thirteen years, disfavor this theory. If dark matter were indeed made up of tiny black holes, the light coming from Icarus would have looked much different.
Since it was discovered in 2016 using the gravitational lensing method, Icarus has provided a new way for astronomers to observe and study individual stars in distant galaxies. In so doing, astronomers are able to get a rare and detailed look at individual stars in the early Universe and see how they (and not just galaxies and clusters) evolved over time.
When the James Webb Space Telescope (JWST) is deployed in 2020, astronomers expect to get an even better look and learn so much more about this mysterious period in cosmic history.
The technique of gravitational lensing relies on the presence of a large cluster of matter between the observer and the object to magnify light coming from that object. Credit: NASA
For the sake of studying the most distant objects in the Universe, astronomers often rely on a technique known as Gravitational Lensing. Based on the principles of Einstein’s Theory of General Relativity, this technique involves relying on a large distribution of matter (such as a galaxy cluster or star) to magnify the light coming from a distant object, thereby making it appear brighter and larger.
However, in recent years, astronomers have found other uses for this technique as well. For instance, a team of scientists from the Harvard-Smithsonian Center for Astrophysics (CfA) recently determined that Gravitational Lensing could also be used to determine the mass of white dwarf stars. This discovery could lead to a new era in astronomy where the mass of fainter objects can be determined.
The study which details their findings, titled “Predicting gravitational lensing by stellar remnants” appeared in the Monthly Noticed of the Royal Astronomical Society. The study was led by Alexander J. Harding of the CfA and included Rosanne Di Stefano, and Claire Baker (also from the CfA), as well as members from the University of Southampton, Georgia State University, the University of Nigeria, and Cornell University.
A Hubble image of the white dwarf star PM I12506+4110E (the bright object, seen in black in this negative print) and its field which includes two distant stars PM12-MLC1&2. Credit: Harding et al./NASA/HST
To put it simply, determining the mass of an astronomical object is one the greatest challenges for astronomers. Until now, the most successful method relied on binary systems because the orbital parameters of these systems depend on the masses of the two objects. Unfortunately, objects that are at the end states of stellar evolution – like black holes, neutron stars or white dwarfs – are often too faint or isolated to be detectable.
This is unfortunate, since these objects are responsible for a lot of dramatic astronomical events. These include the accretion of material, the emission of energetic radiation, gravitational waves, gamma-ray bursts, or supernovae. Many of these events are still a mystery to astronomers or the study of them is still in its infancy – i.e. gravitational waves. As they state in their study:
“Gravitational lensing provides an alternative approach to mass measurement. It has the advantage of only relying on the light from a background source, and can therefore be employed even for dark lenses. In fact, since light from the lens can interfere with the detection of lensing effects, compact objects are ideal lenses.”
As they go on to state, of the 18,000 lensing events that have been detected to date, roughly 10 to 15% are believed to have been caused by compact objects. However, scientists are unable to tell which of the detected events were due to compact lenses. For the sake of their study then, the team sought to circumvent this problem by identifying local compact objects and predicting when they might produce a lensing event so they could be studied.
Animation showing the white dwarf star Stein 2051B as it passes in front of a distant background star. Credit: NASA
“By focusing on pre-selected compact objects in the near vicinity of the Sun, we ensure that the lensing event will be caused by a white dwarf, neutron star, or black hole,” they state. “Furthermore, the distance and proper motion of the lens can be accurately measured prior to the event, or else afterwards. Armed with this information, the lensing light curve allows one to accurately measure the mass of the lens.”
In the end, the team determined that lensing events could be predicted from thousands of local objects. These include 250 neutron stars, 5 black holes, and roughly 35,000 white dwarfs. Neutron stars and black holes present a challenge since the known populations are too small and their proper motions and/or distances are not generally known.
But in the case of white dwarfs, the authors anticipate that they will provide for many lensing opportunities in the future. Based on the general motions of the white dwarfs across the sky, they obtained a statistical estimate that about 30-50 lensing events will take place per decade that could be spotted by the Hubble Space Telescope, the ESA’s Gaia mission, or NASA’s James Webb Space Telescope (JWST). As they state in their conclusions:
“We find that the detection of lensing events due to white dwarfs can certainly be observed during the next decade by both Gaia and HST. Photometric events will occur, but to detect them will require observations of the positions of hundreds to thousands of far-flung white dwarfs. As we learn the positions, distances to, and proper motions of larger numbers of white dwarfs through the completion of surveys such as Gaia and through ongoing and new wide-field surveys, the situation will continue to improve.”
The future of astronomy does indeed seem bright. Between improvements in technology, methodology, and the deployment of next-generation space and ground-based telescopes, there is no shortage of opportunities to see and learn more.
This illustration shows how gravitational lensing works. The gravity of a large galaxy cluster is so strong, it bends, brightens and distorts the light of distant galaxies behind it. The scale has been greatly exaggerated; in reality, the distant galaxy is much further away and much smaller. Credit: NASA, ESA, L. Calcada
When it comes to studying some of the most distant and oldest galaxies in the Universe, a number of challenges present themselves. In addition to being billions of light years away, these galaxies are often too faint to see clearly. Luckily, astronomers have come to rely on a technique known as Gravitational Lensing, where the gravitational force of a large object (like a galactic cluster) is used to enhance the light of these fainter galaxies.
Using this technique, an international team of astronomers recently discovered a distant and quiet galaxy that would have otherwise gone unnoticed. Led by researchers from the University of Hawaii at Manoa, the team used the Hubble Space Telescope to conduct the most extreme case of gravitational lensing to date, which allowed them to observe the faint galaxy known as eMACSJ1341-QG-1.
The quiescent galaxy eMACSJ1341-QG-1 as seen by the Hubble Space Telescope. The yellow dotted line traces the boundaries of the galaxy’s gravitationally lensed image. The inset on the upper left shows what eMACSJ1341-QG-1 would look like if we observed it directly, without the cluster lens. Credit: Harald Ebeling/UH IfA
For the sake of their study, the team relied on the massive galaxy cluster known as eMACSJ1341.9-2441 to magnify the light coming from eMACSJ1341-QG-1, a distant and fainter galaxy. In astronomical terms, this galaxy is an example of a “quiescent galaxy”, which are basically older galaxies that have largely depleted their supplies of dust and gas and therefore do not form new stars.
The team began by taking images of the faint galaxy with the Hubble and then conducting follow-up spectroscopic observations using the ESO/X-Shooter spectrograph – which is part of the Very Large Telescope (VLT) at the Paranal Observatory in Chile. Based on their estimates, the team determined that they were able to amplify the background galaxy by a factor of 30 for the primary image, and a factor of six for the two remaining images.
This makes eMACSJ1341-QG-1 the most strongly amplified quiescent galaxy discovered to date, and by a rather large margin! As Johan Richard – an assistant astronomer at the University of Lyon who performed the lensing calculations, and a co-author on the study – indicated in a University of Hawaii News release:
“The very high magnification of this image provides us with a rare opportunity to investigate the stellar populations of this distant object and, ultimately, to reconstruct its undistorted shape and properties.”
A spiral galaxy ablaze in the blue light of young stars from ongoing star formation (left) and an elliptical galaxy bathed in the red light of old stars (right). Credit: Sloan Digital Sky Survey, CC BY-NC.
Although other extreme magnifications have been conducted before, this discovery has set a new record for the magnification of a rare quiescent background galaxy. These older galaxies are not only very difficult to detect because of their lower luminosity; the study of them can reveal some very interesting things about the formation and evolution of galaxies in our Universe.
As Ebeling, an astronomer with the UH’s Institute of Astronomy and the lead author on the study, explained:
“We specialize in finding extremely massive clusters that act as natural telescopes and have already discovered many exciting cases of gravitational lensing. This discovery stands out, though, as the huge magnification provided by eMACSJ1341 allows us to study in detail a very rare type of galaxy.”
Quiescent galaxies are common in the local Universe, representing the end-point of galactic evolution. As such, this record-breaking find could provide some unique opportunities for studying these older galaxies and determining why star-formation ended in them. As Mikkel Stockmann, a team member from the University of Copenhagen and an expert in galaxy evolution, explained:
“[A]s we look at more distant galaxies, we are also looking back in time, so we are seeing objects that are younger and should not yet have used up their gas supply. Understanding why this galaxy has already stopped forming stars may give us critical clues about the processes that govern how galaxies evolve.”
An artist’s impression of the accretion disc around the supermassive black hole that powers an active galaxy. Credit: NASA/Dana Berry, SkyWorks Digital
In a similar vein, recent studies have been conducted that suggest that the presence of a Supermassive Black Hole (SMBH) could be what is responsible for galaxies becoming quiescent. As the powerful jets these black holes create begin to drain the core of galaxies of their dust and gas, potential stars find themselves starved of the material they would need to undergo gravitational collapse.
In the meantime, follow-up observations of eMACSJ1341-QG1 are being conducted using telescopes at the Paranal Observatory in Chile and the Maunakea Observatories in Hawaii. What these observations reveal is sure to tell us much about what will become of our own Milky Way Galaxy someday, when the last of the dust and gas is depleted and all its stars become red giants and long-lived red dwarfs.
