Images acquired of the Aqua satellite of the sea lanes off the coast of Portugal, taken on January 16th, 2018. Credit: NASA/Jeff Schmaltz, LANCE/EOSDIS Rapid Response
Earth, when viewed from space, is a pretty spectacular thing to behold. From orbit, one can see every continent, landmass, and major feature. Weather patterns are also eerily clear from space, with everything from hurricanes to auroras appearing as a single system. On top of that, it is only from orbit that the full extent of human activity can be truly appreciated.
For instance, when one hemisphere of Earth passes from day into night, one can see the patchwork of urban development by picking out the filamentary structure of lights. And as NASA’s Aqua satellite recently demonstrated with a high-resolution image it captured over the Atlantic Ocean, ships criss-crossing the ocean can also create some beautiful patterns.
As part of the NASA-centered international Earth Observing System (EOS), the Aqua satellite was launched on May 4th, 2002, to collect information on Earth’s water cycle. Using a suite of six Earth-observing instruments, this satellite has gathered global data on ocean evaporation, water vapor in the atmosphere, clouds, precipitation, soil moisture, sea ice, land ice, and snow cover.
NASA’s Aqua Earth-observing satellite. Credit: NASA
The image was acquired on January 16th, 2018, by the Moderate Resolution Imaging Spectroradiometer (MODIS). Pictured in this image are ships off the coast of Portugal and Spain producing cloud trails known as ship tracks. Some of these tracks stretch for hundreds of kilometers and grow broader with distance – i.e. the narrow ends are the youngest while the broader, wavier ends are older.
These clouds form when water vapor condenses around tiny particles of pollution emitted by the ship’s exhaust. This is due to the fact that some particles generated by ships (like sulfates) are soluble in water and seeds clouds. This also causes light hitting these clouds to scatter in many directions, making them appear brighter and thicker than unpolluted maritime clouds (which are seeded by larger particles like sea salt).
As always, seeing things from space provides an incredible sense of perspective. This is especially helpful when attempting to monitor and model something as complex as Earth’s environment and humanity’s impact on it. And of course, it also allows for some breathtaking photos!
Special Guest:
Paul Hildebrandt (director of the film Fight for Space) joins us again to discuss his newest project, a documentary which is an historical piece about the mission of Apollo 8 and it’s crew, Borman, Anders, and Lovell. Titled First to the Moon, the film covers the biographies of each astronaut and goes on to tell the story of the Apollo 8 flight using new animations and newly found archival footage.
Announcements:
If you would like to join the Weekly Space Hangout Crew, visit their site here and sign up. They’re a great team who can help you join our online discussions!
We record the Weekly Space Hangout every Wednesday at 5:00 pm Pacific / 8:00 pm Eastern. You can watch us live on Universe Today, or the Weekly Space Hangout YouTube page – Please subscribe!
This graphic shows atmospheric bow waves forming during the August 2017 eclipse over the continental United States. Image: Shunrong Zhang/Haystack Observatory
It’s long been predicted that a solar eclipse would cause a bow wave in Earth’s ionosphere. The August 2017 eclipse—called the “Great American Eclipse” because it crossed the continental US— gave scientists a chance to test that prediction. Scientists at MIT’s Haystack Observatory used more than 2,000 GNSS (Global Navigation Satellite System) receivers across the continental US to observe this type of bow wave for the first time.
The Great American Eclipse took 90 minutes to cross the US, with totality lasting only a few minutes at any location. As the Moon’s shadow moved across the US at supersonic speeds, it created a rapid temperature drop. After moving on, the temperature rose again. This rapid heating and cooling is what caused the ionospheric bow wave.
The bow wave itself is made up of fluctuations in the electron content of the ionosphere. The GNSS receivers collect very accurate data on the TEC (Total Electron Content) of the ionosphere. This animation shows the bow wave of electron content moving across the US.
The details of this bow wave were published in a paper by Shun-Rong Zhang and colleagues at MIT’s Haystack Observatory, and colleagues at the University of Tromso in Norway. In their paper, they explain it like this: “The eclipse shadow has a supersonic motion which [generates] atmospheric bow waves, similar to a fast-moving river boat, with waves starting in the lower atmosphere and propagating into the ionosphere. Eclipse passage generated clear ionospheric bow waves in electron content disturbances emanating from totality primarily over central/eastern United States. Study of wave characteristics reveals complex interconnections between the sun, moon, and Earth’s neutral atmosphere and ionosphere.”
The ionosphere stretches from about 50 km to 1000 km in altitude during the day. It swells as radiation from the Sun reaches Earth, and subsides at night. Its size is always fluctuating during the day. It’s called the ionosphere because it’s the region where charged particles created by solar radiation reside. The ionosphere is also where auroras occur. But more importantly, it’s where radio waves propagate.
The ionosphere surrounds the Earth, extending from about 80 km to 650 km. Image Credit: NASA’s Goddard Space Flight Center/Duberstein
The ionosphere plays an important role in the modern world. It allows radio waves to travel over the horizon, and also affects satellite communications. This image shows some of the complex ways our communications systems interact with the ionosphere.
This graphic shows some of the effects that the ionosphere has on communications. Image: National Institute of Information and Communications Technology
There’s a lot going on in the ionosphere. There are different types of waves and disturbances besides the bow wave. A better understanding of the ionosphere is important in our modern world, and the August eclipse gave scientists a chance not only to observe the bow wave, but also to study the ionosphere in greater detail.
The GNSS data used to observe the bow wave was key in another study as well. This one was also published in the journal Geophysical Research Letters, and was led by Anthea Coster of the Haystack Observatory. The data from the network of GNSS was used to detect the Total Electron Content (TEC) and the differential TEC. They then analyzed that data for a couple things during the passage of the eclipse: the latitudinal and longitudinal response of the TEC, and the presence of any Travelling Ionospheric Disturbances (TID) to the TEC.
Predictions showed a 35% reduction in TEC, but the team was surprised to find a reduction of up to 60%. They were also surprised to find structures of increased TEC over the Rocky Mountains, though that was never predicted. These structures are probably linked to atmospheric waves created in the lower atmosphere by the Rocky Mountains during the solar eclipse, but their exact nature needs to be investigated.
This image of GNSS data shows the positive Travelling Ionospheric Disturbance (TID) structure in the center of the primary TEC depleted region. The triangles mark cities in or near the Rocky Mountains. Image: Coster et. al.
“… a giant active celestial experiment provided by the sun and moon.” – Phil Erickson, assistant director at Haystack Observatory.
“Since the first days of radio communications more than 100 years ago, eclipses have been known to have large and sometimes unanticipated effects on the ionized part of Earth’s atmosphere and the signals that pass through it,” says Phil Erickson, assistant director at Haystack and lead for the atmospheric and geospace sciences group. “These new results from Haystack-led studies are an excellent example of how much still remains to be learned about our atmosphere and its complex interactions through observing one of nature’s most spectacular sights — a giant active celestial experiment provided by the sun and moon. The power of modern observing methods, including radio remote sensors distributed widely across the United States, was key to revealing these new and fascinating features.”
The Great American Eclipse has come and gone, but the detailed data gathered during that 90 minute “celestial experiment” will be examined by scientists for some time.
A view of mountains and glaciers in Antarctica’s Marie Byrd Land seen during the Nov. 2, 2014, IceBridge survey flight. Credit: NASA / Michael Studinger
One of the benefits of the Space Age is the way it has allowed human beings to see Earth in all of its complexity and splendor. In addition, it has allowed us to conduct studies of Earth’s surface and atmosphere from orbit, which helps us to see the impact we have on our the planet. It is with this purpose in mind that NASA’s Earth Observation Program has been monitoring the Arctic and Antarctic for many years.
For instance, Operation IceBridge has spent much of the past decade monitoring the Antarctic ice sheet for signs of cracks and flows. The purpose of this is to determine how and at what rate the ice sheet is changing due to Climate Change. Recently, NASA crews conducted a flight over the southern Antarctic Peninsula as part of Operation IceBridge ninth year, which resulted in some stunning pictures of the icy landscape.
The flight took place on November 4th, 2017, as part of IceBridge’s “Endurance West” mission to study sea ice. The path they chose follows the ground track of NASA’s Ice, Cloud, and land Elevation Satellite-2 (ICESat-2), an ice-mapping satellite that is scheduled for launch in late 2018. This path began at the northern tip of the Antarctic Peninsula and then moved southward across the Weddell Sea.
Semi-permanent cracks on the Antarctic Peninsula. Credit: NASA/Digital Mapping System.
The images the crew took aboard their P3 research plane were captured by a Digital Mapping System, a downward-pointing camera that collects thousands of high-resolution photographs during a single flight. While traveling over the southern Antarctic Peninsula, they imaged a landscape that resembled rapids, where the motion of rivers becomes amplified as the water flows through steeper, narrower terrain.
In a similar fashion, as ice flows through narrower canyons and down steeper bedrock, more fractures appear at the surface. But of course, the rate at which this takes place is much slower, which can make discerning movement in the ice sheet rather difficult. The first image (shown above) shows ice flowing into the southern part of the George VI ice shelf, which is located in Palmer Land south of the Seward Mountains.
In this location, cracks are likely to be a regular feature that form as the ice flows over the bedrock. However, since the ice flow is relatively slow (even on the steeper part of the bedrock), the surface cracks are not as dramatic as in other regions. For example, the second image (shown below), which shows a heavily crevassed glacier that measures about 21 km (13 mi) long and 11 km (7 mi) wide.
The glacier appears to be flowing west from the Dyer Plateau to George VI Sound while the north side merges with the Meiklejohn Glacier. The third image (bottom) shows a heavily crevassed glacier north of Creswick Peaks that also flows west into George VI Sound. In short, the pictures confirm that ice on the southern end of the Antarctic Peninsula is flowing towards the ocean.
A heavily crevassed glacier flows west from the Dyer Plateau. Credit: NASA/Digital Mapping System
The purpose of IceBridge, which has been conducting regular measurements in the Antarctic Peninsula since 2009, has been to study just how fast and to what extent Climate Change has been impacting the region. While ice sheet loss is a well-documented phenomenon, scientists have known for some time that the most dramatic losses in Antarctica occur along its western side.
In addition, research has shown that the southern part of the peninsula is particularly vulnerable, as the glaciers and ice shelves there have become destabilized and are slowly feeding into the sea. And unlike sea ice, the land ice in this region has the potential to raise sea levels around the world. As Michael Studinger, the project manager for IceBridge, describes the operation:
“IceBridge exists because we need to understand how much ice the Greenland and Antarctic ice sheets will contribute to sea level rise over the next couple of decades. In order to do this, we need to measure how much the ice surface elevation is changing from year to year.”
Knowing how significant the impact of Climate Change will be is the first step in developing countermeasures. It also serves as a stark reminder that the problem exists, and that solutions need to be found before it is too late.
The proposed "space-tie" propulsion system being patented by Spanish scientists could be useful on Satellites like the ESA's Sentinel-1, pictured. Image: ESA/ATG
Some of the best things in science are elegant and simple. A new propulsion system being developed in Spain is both those things, and could help solve a growing problem with Earth’s satellites: the proliferation of space junk.
Researchers at Universidad Carlos III de Madrid (UC3M) and the Universidad Politécnica de Madrid (UPM) in Spain are patenting a new kind of propulsion system for orbiting satellites that doesn’t use any propellant or consumables. The system is basically a tether, in the form of an aluminum tape a couple kilometers long and a couple inches wide, that trails out from the satellite. The researchers call it a space tie.
“This is a disruptive technology because it allows one to transform orbital energy into electrical energy and vice versa without using any type of consumable”. – Gonzalo Sánchez Arriaga, UC3M.
The lightweight space tie is rolled up during launch, and once the satellite is in orbit, it’s deployed. Once deployed, the tape can either convert electricity into thrust, or thrust into electricity. The Spanish researchers behind this say that the space-ties will be used in pairs.
The system is based on what is called a “low-work-function” tether. A special coating on the tether has enhanced electron emission properties on receiving sunlight and heat. These special properties allow it to function in two ways. “This is a disruptive technology because it allows one to transform orbital energy into electrical energy and vice versa without using any type of consumable,” said Gonzalo Sánchez Arriaga, Ramón y Cajal researcher at the Bioengineering and Aerospace Engineering Department at UC3M.
As a satellite loses altitude and gets closer to Earth, the tether converts that thrust-caused-by-gravity into electricity for the spacecraft systems to use. When it comes to orbiting facilities like the International Space Station (ISS), this tether system could solve an annoying problem. Every year the ISS has to burn a significant amount of propellant to maintain its orbit. The tether can generate electricity as it moves closer to Earth, and this electricity could replace the propellant. “With a low- work function tether and the energy provided by the solar panel of the ISS, the atmospheric drag could be compensated without the use of propellant”, said Arriaga.
“Unlike current propulsion technologies, the low-work function tether needs no propellant and it uses natural resources from the space environment such as the geomagnetic field, the ionospheric plasma and the solar radiation.” – Gonzalo Sánchez Arriaga, UC3M.
For satellites with ample on-board power, the tether would operate in reverse. It would use electricity to provide thrust to the space craft. This is especially useful to satellites near the end of their operational life. Rather than languish in orbit for a long time as space junk, the derelict satellite could be forced to re-enter Earth’s atmosphere where it would burn up harmlessly.
The space-tie system is based on what’s called Lorentz drag. Lorentz drag is an electrodynamic effect. (Electrodynamics enthusiasts can read all about it here.) I won’t go too deeply into it because I’m not a physicist, but the Spanish researchers suggest that the Lorentz drag can be easily observed by watching a magnet fall through a copper tube. Here’s a video.
Space organizations have shown interest in the low-work-function tether, and the Spanish team is getting the word out to experts in the USA, Japan, and Europe. The next step is the manufacture of prototypes. “The biggest challenge is its manufacturing because the tether should gather very specific optical and electron emission properties,” says Sánchez Arriaga.
The Spanish Ministry of Economy, Industry and Competitiveness has awarded the Spanish team a grant to investigate materials for the system. The team has also submitted a proposal to the European Commission’s Future and Emerging Technologies (FET-Open) consortium for funding. “The FET-OPEN project would be foundational because it considers the manufacturing and characterization of the first low-work-function tether and the development of a deorbit kit based on this technology to be tested on a future space mission. If funded, it would be a stepping stone to the future of low-work-function tethers in space” Sanchez Arriaga concluded.
In this video, Gonzalo Sanchez Arriaga explains how the system works. If you don’t speak Spanish, just turn on subtitles.
Using the microlensing metthod, a team of astrophysicists have found the first extra-galactic planets! Credit: NASA/Tim Pyle
The study of exoplanets has advanced by leaps and bounds in the past few decades. Between ground-based observatories and spacecraft like the Kepler mission, a total of 3,726 exoplanets have been confirmed in 2,792 systems, with 622 systems having more than one planet (as of Jan. 1st, 2018). And in the coming years, scientists expect that many more discoveries will be possible thanks to the deployment of next-generation missions.
These include NASA’sJames Webb Space Telescope (JWST) and several next-generation ground based observatories. With their advanced instruments, these and other observatories are not only expected to find many more exoplanets, but to reveal new and fascinating things about them. For instance, a recent study from Columbia University indicated that it will be possible, using the Transit Method, to study surface elevations on exoplanets.
The study, which recently appeared online under the title “Finding Mountains with Molehills: The Detectability of Exotopography“, was conducted by Moiya McTier and David Kipping – and graduate student and an Assistant Professor of Astronomy at Columbia University, respectively. Based on models they created using bodies in our Solar System, the team considered whether transit surveys might be able to reveal topographical data on exoplanets.
Artist’s impression of an extra-solar planet transiting its star. Credit: QUB Astrophysics Research Center
To recap, the Transit Method (aka. Transit Photometry) is currently the most popular and reliable means for detecting exoplanets. It consists of astronomers measuring the light curve of distant stars over time and looking for periodic dips in brightness. These dips are the result of exoplanets passing in front of the star (i.e. transiting) relative to the observer.
By measuring the rate at which the star’s light dips, and the period with which the dimming occurs, astronomer are not only able to determine the presence of exoplanets, but also place accurate constraints on their size and orbital periods. According to McTier and Kipping, this same method could also reveal the presence of geographical features – for instance, mountain ranges, volcanoes, trenches, and craters.
As they indicate in their study, in lieu of direct imaging, indirect methods are the only means astronomers have for revealing data on an exoplanet’s surface. Unfortunately, there is no conceivable way that the radial velocity, microlensing, astrometry, and timing methods could reveal exotopography. This leaves the transit method, which has some potential in this respect. As they state:
“The transit method directly measures the sky-projected area of a planet’s silhouette relative to that of a star, under the assumption that the planet is not luminous itself… This fact implies that there is indeed some potential for transits to reveal surface features, since the planet’s silhouette is certainly distorted from a circular profile due to the presence of topography.”
Satellite image of the Himalayan mountain chain, as imaged by NASA’sLandsat-7 imagery of Himalayas. Credit: NASA
In other words, as a planet transits in front of its host star, the light passing around the planet itself could be measured for small variations. These could indicate the presence of mountain ranges and other large-scale features like massive chasms. To test this theory, they considered planets in the Solar System as templates for how the scattering of light during a transit could reveal large-scale features.
As an example, they consider what an Earth analog planet would reveal if the Himalayan mountain range ran from north to south and was wide enough to span 1° in longitude:
“Now assume that the planet completes half of one rotation as it transits its parent star from our point of view, which is all that is necessary to see all of the planet’s features appear on its silhouette without repeating. As our hypothetical planet rotates and the Himalayan block moves into and out of view, the change in silhouette will result in different transit depths…”
Ultimately, they consider that Mars would be the ideal test case due to its combination of small size, low surface gravity, and active internal volcanism, which has caused it become what they describe as the “bumpiest body in the Solar System”. When paired with a white dwarf star, this presents the optimal case for using light curves to determine exotopography.
Color mosaic of Mars’ greatest mountain, Olympus Mons, viewed from orbit. Credit NASA/JPL
At a distance of about 0.01 AU (which would be within a white dwarf’s habitable zone), they calculate that a Mars-sized planet would have an orbital period of 11.3 hours. This would allow for many transits to be observed in a relatively short viewing period, thus ensuring a greater degree of accuracy. At the same time, the team admits that their proposed methods suffers from drawbacks.
For instance, due to the presence of astrophysical and instrumental noise, they determined that their method would be unproductive when it comes to studying exoplanets around Sun-like stars and M-type (red dwarf) stars. But for Mars-like planets orbiting low mass, white dwarf stars, the method could produce some highly valuable scientific returns.
While this might sound rather limited, it would present some rather fascinating opportunities to learn more about planets beyond our Solar System. As they explain:
“Finding the first evidence of mountains on planets outside our solar system would be exciting in its own right, but we can also infer planet characteristics from the presence and distribution of surface features. For example, a detection of bumpiness could lead to constraints on a planet’s internal processes.”
In short, planets with a high degree of bumpiness would indicate tectonic activity or the buildup of lava caused by internal heating sources. Those with the highest bumpiness (i.e. like Mars) would indicate that they too experience a combination internal processes, low surface gravity, volcanism, and a lack of tectonic plate movement. Meanwhile, low-bumpiness planets are less likely to have any of these internal processes and their surfaces are more likely to be shaped by external factors – like asteroid bombardment.
Artist’s impression of the OWL Telescope being deployed at night from its enclosure, where it will operated during the daytime. Credit: ESO
Based on their estimates, they conclude that the various super telescopes that are scheduled to be commissioned in the coming years would be up to task. These include the ESO’s OverWhelmingly Large (OWL) Telescope, a 100-meter proposed optical and near-infrared telescope that would build on the success of the Very Large Telescope (VLT) and the upcoming Extremely Large Telescope (ELT).
Another example is the Colossus Telescope, a 74-meter optical and infrared telescope that is currently being commissioned by an international consortium. Once operational, it will be the largest telescope optimized for detecting extrasolar life and extraterrestrial civilizations.
In the past, the success of exoplanet hunters has come down to a combination of factors. In addition to greater levels of cooperation between institutions, amateur astronomers and citizen scientists, there has also been the way in which improved technology has coincided with new theoretical models. As more data become available, scientists are able to produce more educated estimates on what we might be able to learn once new instruments come online.
When the next-generation telescopes take to space or are finished construction here on Earth, we can anticipate that thousands more exoplanets will be found. At the same time, we can anticipate that important details will be also discovered about these planets that were not possible before. Do they have atmospheres? Do they have oceans? Do they have mountain ranges and chasms? We hope to find out!
You know what’s fun? Mysteries. Here’s one: fast radio bursts. Astronomers have been detecting mysterious one-time signals from across the sky. What’s causing them? Nobody knows for sure, but the search is on to get to the bottom of them.
If you would like to join the Weekly Space Hangout Crew, visit their site here and sign up. They’re a great team who can help you join our online discussions!
Artist's illustration of two merging neutron stars. The narrow beams represent the gamma-ray burst while the rippling spacetime grid indicates the isotropic gravitational waves that characterize the merger. Swirling clouds of material ejected from the merging stars are a possible source of the light that was seen at lower energies. Credit: National Science Foundation/LIGO/Sonoma State University/A. Simonnet
In August of 2017, a major breakthrough occurred when scientists at the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected gravitational waves that were believed to be caused by the collision of two neutron stars. This source, known as GW170817/GRB, was the first gravitational wave (GW) event that was not caused by the merger of two black holes, and was even believed to have led to the formation of one.
As such, scientists from all over the world have been studying this event ever since to learn what they can from it. For example, according to a new study led by the McGill Space Institute and Department of Physics, GW170817/GRB has shown some rather strange behavior since the two neutron stars colliding last August. Instead of dimming, as was expected, it has been gradually growing brighter.
Chandra images showing the X-ray afterglow of the GW170817/GRB event. Credit: NASA/CXC/McGill University/J. Ruan et al.
For the sake of their study, the team relied on data obtained by NASA’s Chandra X-ray Observatory, which showed that the remnant has been brightening in the X-ray and radio wavelengths in the months since the collision took place. As Daryl Haggard, an astrophysicist with McGill University whose research group led the new study, said in a recent Chandra press release:
“Usually when we see a short gamma-ray burst, the jet emission generated gets bright for a short time as it smashes into the surrounding medium – then fades as the system stops injecting energy into the outflow. This one is different; it’s definitely not a simple, plain-Jane narrow jet.”
What’s more, these X-ray observations are consistent with radiowave data reported last month by another team of scientists, who also indicated that it was continuing to brighten during the three months since the collision. During this same period, X-ray and optical observatories were unable to monitor GW170817/GRB because it was too close to the Sun at the time.
However, once this period ended, Chandra was able to gather data again, which was consistent with these other observations. As John Ruan explained:
“When the source emerged from that blind spot in the sky in early December, our Chandra team jumped at the chance to see what was going on. Sure enough, the afterglow turned out to be brighter in the X-ray wavelengths, just as it was in the radio.”
Collisions of neutron stars produce powerful gamma-ray bursts – and heavy elements like gold (Credit: Dana Berry, SkyWorks Digital, Inc.)
This unexpected behavior has led to a serious buzz in the scientific community, with astronomers trying to come up with explanations as to what type of physics could be driving these emissions. One theory is a complex model for neutron star mergers known as “cocoon theory”. In accordance with this theory, the merger of two neutron stars could trigger the release of a jet that shock-heats the surrounding gaseous debris.
This hot “cocoon” around the jet would glow brightly, which would explain the increase in X-ray and radiowave emissions. In the coming months, additional observations are sure to be made for the sake of confirming or denying this explanation. Regardless of whether or not the “cocoon theory” holds up, any and all future studies are sure to reveal a great deal more about this mysterious remnant and its strange behavior.
As Melania Nynka, another McGill postdoctoral researcher and a co-author on the paper indicated, GW170817/GRB presents some truly unique opportunities for astrophysical research. “This neutron-star merger is unlike anything we’ve seen before,” she said. “For astrophysicists, it’s a gift that seems to keep on giving.”
It is no exaggeration to say that the first-ever detection of gravitational waves, which took place in February of 2016, has led to a new era in astronomy. But the detection of two neutron stars colliding was also a revolutionary accomplishment. For the first time, astronomers were able to observe such an event in both light waves and gravitational waves.
In the end, the combination of improved technology, improved methodology, and closer cooperation between institutions and observatories is allowing scientists to study cosmic phenomena that was once merely theoretical. Looking ahead, the possibilities seem almost limitless!
Artist's impression of the star cluster NGC 3201 orbiting an black hole with about four times the mass of the Sun. Credit: ESO/L. Calçada
Astronomers have been fascinated with globular clusters ever since they were first observed in 17th century. These spherical collections of stars are among the oldest known stellar systems in the Universe, dating back to the early Universe when galaxies were just beginning to grow and evolve. Such clusters orbit the centers of most galaxies, with over 150 known to belong to the Milky Way alone.
One of these clusters is known as NGC 3201, a cluster located about 16,300 light years away in the southern constellation of Vela. Using the ESO’s Very Large Telescope (VLT) at the Paranal Observatory in Chile, a team of astronomers recently studied this cluster and noticed something very interesting. According to the study they released, this cluster appears to have a black hole embedded in it.
For the sake of their study, the team relied on the Multi Unit Spectroscopic Explorer (MUSE) instrument on the VLT to observe NGC 3201. This instrument is unique because of the way it allows astronomers to measure the motions of thousands of far away stars simultaneously. In the course of their observations, the team found that one of the cluster’s stars was being flung around at speeds of several hundred kilometers an hour and with a period of 167 days.
“It was orbiting something that was completely invisible, which had a mass more than four times the Sun — this could only be a black hole! The first one found in a globular cluster by directly observing its gravitational pull.”
This finding was rather unexpected, and constitutes the first time that astronomers have been able to detect an inactive black hole at the heart of a globular cluster – meaning that it is not currently accreting matter or surrounded by a glowing disc of gas. They were also able to estimate the black hole’s mass by measuring the movements of the star around it and thus extrapolating its enormous gravitational pull.
From its observed properties, the team determined that the rapidly-moving star is about 0.8 times the mass of our Sun and the mass of its black hole counterpart to be around 4.36 times the Sun’s mass. This put’s it in the “stellar-mass black hole” category, which are stars that exceeds the maximum mass allowance of a neutron star, but are smaller than supermassive black holes (SMBHs) – which exist at the centers of most galaxies.
This finding is highly significant, and not just because it was the first time that astronomers have observed a stellar-mass black hole in a globular cluster. In addition, it confirms what scientists have been suspecting for a few years now, thanks to recent radio and x-ray studies of globular clusters and the detection of gravity wave signals. Basically, it indicates that black holes are more common in globular clusters than previously thought.
“Until recently, it was assumed that almost all black holes would disappear from globular clusters after a short time and that systems like this should not even exist!” said Giesers. “But clearly this is not the case – our discovery is the first direct detection of the gravitational effects of a stellar-mass black hole in a globular cluster. This finding helps in understanding the formation of globular clusters and the evolution of black holes and binary systems – vital in the context of understanding gravitational wave sources.”
This find was also significant given that the relationship between black holes and globular clusters remains a mysterious, but highly important one. Due to their high masses, compact volumes, and great ages, astronomers believe that clusters have produced a large number of stellar-mass black holes over the course of the Universe’s history. This discovery could therefore tell us much about the formation of globular clusters, black holes, and the origins of gravitational wave events.
And be sure to enjoy this ESO podcast explaining the recent discovery:
