Our galaxy has about 200 Globular Clusters (GCs,) and most of them are in the galaxy’s halo. Astronomers think most GCs were taken from dwarf galaxies and merged with the Milky Way due to the galaxy’s powerful gravity. That explains why so many of them are on the outskirts of the galaxy. But they’re not all in the halo. Some are towards the Milky Way’s galactic bulge. What are globular clusters doing there?Continue reading “The Hubble Imaged Some Globular Clusters in an Unusual Place: Near the Milky Way’s Centre”
It has been over sixty years since the first Search for Extraterrestrial Intelligence (SETI) survey occurred. This was Project Ozma, a survey led by Dr. Frank Drake (who devised the Drake Equation) that used the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, to listen for radio transmissions from Epsilon Eridani and Tau Ceti. While the search revealed nothing of interest, it paved the way for decades of research, theory, and attempts to find evidence of technological activity (aka. “technosignatures”).
The search continues today, with researchers using next-generation instruments and analytical methods to find the “needle in the cosmic haystack.” This is the purpose behind Breakthrough Listen Investigation for Periodic Spectral Signals (BLIPSS), a collaborative SETI project led by Cornell graduate student Akshay Suresh to look for technosignatures at the center of the Milky Way. In a recent paper, Suresh and his team shared their initial findings, which were made possible thanks to data obtained by the Greenbank Observatory and a proprietary algorithm they developed.Continue reading “Astronomers are Searching for a Galaxy-Wide Transmitter Beacon at the Center of the Milky Way”
It all began with the discovery of Sagittarius A*, a persistent radio source located at the Galactic Center of the Milky Way that turned out to be a supermassive black hole (SMBH). This discovery was accompanied by the realization that SMBHs exist at the heart of most galaxies, which account for their energetic nature and the hypervelocity jets extending from their center. Since then, scientists have been trying to get a better look at Sag A* and its surroundings to learn more about the role SMBHs play in the formation and evolution of our galaxy.
This has been the goal of the GRAVITY collaboration, an international team of astronomers and astrophysicists that have been studying the core of the Milky Way for the past thirty years. Using the ESO’s Very Large Telescope Interferometer (VLTI), this team obtained the deepest and sharpest images to date of the region around Sag A*. These observations led to the most precise measurement yet of the black hole’s mass and revealed a never-before-seen star that orbits close to it.Continue reading “Best Image Ever Taken of Stars Buzzing Around the Milky Way’s Supermassive Black Hole”
The center of the Milky Way is a mysterious place. Astronomers think there’s a supermassive black hole there, though it could be dark matter instead. The region is densely packed with stars, dominated by red giants. And because of all the dust between Earth and the galactic center, we can’t see anything with visible light, ultraviolet light, or low-energy x-rays.
But we can detect radio waves, and there are some unexplained ones coming from the center of the galaxy, and adding to the mystery.Continue reading “What’s Causing the Mysterious Radio Waves Coming From the Center of the Milky Way?”
The core of the Milky Way Galaxy (aka. Galactic Center), the region around which the rest of the galaxy revolves, is a strange and mysterious place. It is here that the Supermassive Black Hole (SMBH) that powers the compact radio source known as Sagittarius A* is located. It is also the most compact region in the galaxy, with an estimated 10 million stars within 3.26 light-years of the Galactic Center.
Using data from Chandra X-ray Observatory and the MeerKAT radio telescope, NASA and the National Research Foundation (NSF) of South Africa created a mosaic of the center of the Milky Way. Combining images taken in the x-ray and radio wavelengths, the resulting panoramic image manages to capture the filaments of super-heated gas and magnetic fields that (when visualized) shows the complex web of energy at the center of our galaxy.Continue reading “New Mosaic Shows the Galactic Core From Opposite Sides of the Electromagnetic Spectrum”
For years astronomers have puzzled over a strange excess of gamma rays coming from the galactic center. Annihilating dark matter has always been a tantalizing explanation, and new research claims that it’s the best answer.Continue reading “Is Dark Matter Responsible for Extra Gamma Rays Coming From the Center of the Milky Way?”
The heart of the Milky Way can be a mysterious place. A gigantic black hole resides there, and it’s surrounded by a retinue of stars that astronomers call a Nuclear Star Cluster (NSC). The NSC is one of the densest populations of stars in the Universe. There are about 20 million stars in the innermost 26 light years of the galaxy.
New research shows that about 7% of the stars in the NSC came from a single source: a globular cluster of stars that fell into the Milky Way between 3 and 5 billion years ago.Continue reading “7% of the Stars in the Milky Way’s Center Came From a Single Globular Cluster That Got Too Close and Was Broken Up”
At the center of our galaxy lies a region where roughly 10 million stars are packed into just 1 parsec (3.25 light-years) of space. At the center of this lies the supermassive black hole (SMBH) known as Sagittarius A*, which has a mass of over 4 million Suns. For decades, astronomers have been trying to get a better look at this region in the hopes of understanding the incredible forces at work and how they have affected the evolution of our galaxy.
What they’ve found includes a series of stars that orbit very closely to Sagittarius A* (like S1 and S2), which have been used to test Einstein’s Theory of General Relativity. And recently, a team from UCLA’s Galactic Center Orbits Initiative detected a series of compact objects that also orbit the SMBH. These objects look like clouds of gas but behave like stars, depending on how close they are in their orbits to Sagittarius A*.Continue reading “More Mysterious Space Blobs Have Been Found Near the Center of the Milky Way”
During the 1970s, astronomer became aware of a massive radio source at the center of our galaxy that they later realized was a Supermassive Black Hole (SMBH) – which has since been named Sagittarius A*. And in a recent survey conducted by NASA’s Chandra X-ray Observatory, astronomers discovered evidence for hundreds or even thousands of black holes located in the same vicinity of the Milky Way.
But, as it turns out, the center of our galaxy has more mysteries that are just waiting to be discovered. For instance, a team of astronomers recently detected a number of “mystery objects” that appeared to be moving around the SMBH at Galactic Center. Using 12 years of data taken from the W.M. Keck Observatory in Hawaii, the astronomers found objects that looked like dust clouds but behaved like stars.
The research was conducted through a collaboration between Randy Campbell at the W.M. Keck Observatory, members of the Galactic Center Group at UCLA (Anna Ciurlo, Mark Morris, and Andrea Ghez) and Rainer Schoedel of the Instituto de Astrofisica de Andalucia (CSIC) in Granada, Spain. The results of this study were presented at the 232nd American Astronomical Society Meeting during a press conference titled “The Milky Way & Active Galactic Nuclei”.
As Ciurlo explained in a recent W.M. Keck press release:
“These compact dusty stellar objects move extremely fast and close to our Galaxy’s supermassive black hole. It is fascinating to watch them move from year to year. How did they get there? And what will they become? They must have an interesting story to tell.”
The researchers made their discovery using 12 years of spectroscopic measurements obtained by the Keck Observatory’s OH-Suppressing Infrared Imaging Spectrograph (OSIRIS). These objects – which were designed as G3, G4, and G5 – were found while examining the gas dynamics of the center of our galaxy, and were distinguished from background emissions because of their movements.
“We started this project thinking that if we looked carefully at the complicated structure of gas and dust near the supermassive black hole, we might detect some subtle changes to the shape and velocity,” explained Randy Campbell. “It was quite surprising to detect several objects that have very distinct movement and characteristics that place them in the G-object class, or dusty stellar objects.”
Astronomers first discovered G-objects in proximity to Sagittarius A* more than a decade ago – G1 was discovered in 2004 and G2 in 2012. Initially, both were thought to be gas clouds until they made their closest approach to the supermassive black hole and survived. Ordinarily, the SMBHs gravitational pull would shred gas clouds apart, but this did not happen with G1 and G2.
Because these newly discovered infrared sources (G3, G4, and G5) shared the physical characteristics of G1 and G2, the team concluded that they could potentially be G-objects. What makes G-objects unusual is their “puffiness”, where they appear to be cloaked in a layer of dust and gas that makes them difficult to detect. Unlike other stars, astronomers only see a glowing envelope of dust when looking at G-objects.
To see these objects clearly through their obscuring envelope of dust and gas, Campbell developed a tool called the OSIRIS-Volume Display (OsrsVol). As Campbell described it:
“OsrsVol allowed us to isolate these G-objects from the background emission and analyze the spectral data in three dimensions: two spatial dimensions, and the wavelength dimension that provides velocity information. Once we were able to distinguish the objects in a 3-D data cube, we could then track their motion over time relative to the black hole.”
UCLA Astronomy Professor Mark Morris, a co-principal investigator and fellow member of UCLA’s Galactic Center Orbits Initiative (GCOI), was also involved in the study. As he indicated:
“If they were gas clouds, G1 and G2 would not have been able to stay intact. Our view of the G-objects is that they are bloated stars – stars that have become so large that the tidal forces exerted by the central black hole can pull matter off of their stellar atmospheres when the stars get close enough, but have a stellar core with enough mass to remain intact. The question is then, why are they so large?
After examining the objects, the team noticed that there was a great deal of energy was emanating from them, more than what would be expected from typical stars. As a result, they theorized that these G-objects are the result of stellar mergers, which occur when two stars that orbit each other (aka. binaries) crash into each other. This would have been caused by the long-term gravitational influence of the SMBH.
The resulting single object would be distended (i.e. swell up) over the course of millions of years before it finally settled down and appeared like a normal-sized star. The combined objects that resulted from these violent mergers could explain where the excess energy came from and why they behave like stars do. As Andrea Ghez, the founder and director of GCOI, explained:
“This is what I find most exciting. If these objects are indeed binary star systems that have been driven to merge through their interaction with the central supermassive black hole, this may provide us with insight into a process which may be responsible for the recently discovered stellar mass black hole mergers that have been detected through gravitational waves.”
Looking ahead, the team plans to continue following the size and shape of the G-objects’ orbits in the hopes of determining how they formed. They will be paying especially close attention when these stellar objects make their closest approach to Sagittarius A*, since this will allow them to further observe their behavior and see if they remain intact (as G1 and G2 did).
This will take a few decades, with G3 making its closest pass in 20 years and G4 and G5 taking decades longer. In the meantime, the team hopes to learn more about these “puffy” star-like objects by following their dynamical evolution using Keck’s OSIRIS instrument. As Ciurlo stated:
“Understanding G-objects can teach us a lot about the Galactic Center’s fascinating and still mysterious environment. There are so many things going on that every localized process can help explain how this extreme, exotic environment works.”
And be sure to check out this video of the presentation, which takes place from 18:30 until 30:20:
Further Reading: Keck Observatory
In 2013, the European Space Agency deployed the long-awaited Gaia space observatory. As one of a handful of next-generation space observatories that will be going up before the end of the decade, this mission has spent the past few years cataloging over a billion astronomical objects. Using this data, astronomers and astrophysicists hope to create the largest and most precise 3D map of the Milky Way to date.
Though it is almost to the end of its mission, much of its earliest information is still bearing fruit. For example, using the mission’s initial data release, a team of astrophysicists from the University of Toronto managed to calculate the speed at which the Sun orbits the Milky Way. From this, they were able to obtain a precise distance estimate between our Sun and the center of the galaxy for the first time.
For some time, astronomers have been unsure as to exactly how far our Solar System is from the center of our galaxy. Much of this has to do with the fact that it is impossible to view it directly, due to a combination of factors (i.e. perspective, the size of our galaxy, and visibility barriers). As a result, since the year 2000, official estimates have varied between 7.2 and 8.8 kiloparsecs (~23,483 to 28,700 light years).
For the sake of their study, the team – which was led by Jason Hunt, a Dunlap Fellow at the Dunlap Institute for Astronomy & Astrophysics at the University of Toronto – combined Gaia’s initial release with data from the RAdial Velocity Experiment (RAVE). This survey, which was conducted between 2003 and 2013 by the Australian Astronomical Observatory (AAO), measured the positions, distances, radial velocities and spectra of 500,000 stars.
Over 200,000 of these stars were also observed by Gaia and information on them was included in its initial data release. As they explain in their study, which was published in the Journal of Astrophysical Letters in November 2016, they used this to examined the speeds at which these stars orbit the center of the galaxy (relative to the Sun), and in the process discovered that there was an apparent distribution in their relative velocities.
In short, our Sun moves around the center of the Milky Way at a speed of 240 km/s (149 mi/s), or 864,000 km/h (536,865 mph). Naturally, some of the more than 200,000 candidates were moving faster or slower. But for some, there was no apparent angular momentum, which they attributed to these stars being scattering onto “chaotic, halo-type orbits when they pass through the Galactic nucleus”.
As Hunt explained in Dunlap Institute press release:
“Stars with very close to zero angular momentum would have plunged towards the Galactic center where they would be strongly affected by the extreme gravitational forces present there. This would scatter them into chaotic orbits taking them far above the Galactic plane and away from the Solar neighbourhood… By measuring the velocity with which nearby stars rotate around our Galaxy with respect to the Sun, we can observe a lack of stars with a specific negative relative velocity. And because we know this dip corresponds to 0 km/sec, it tells us, in turn, how fast we are moving.”
The next step was to combine this information with proper motion calculations of Sagittarius A* – the supermassive black hole believed to be at the center of our galaxy. After correcting for its motion relative to background objects, they were able to effectively triangulate the Earth’s distance from the center of the galaxy. From this, they derived a refined distance of estimate of 7.6 to 8.2 kpc – which works out to about 24,788 to 26,745 light years.
This study builds upon previous work conducted by the study’s co-authors – Prof. Ray Calberg, the current chair of the Department of Astronomy & Astrophysics at the University of Toronto. Years ago, he and Prof. Kimmo Innanen of the Department of Physics and Astronomy at York University conducted a similar study using radial velocity measurement from 400 of the Milky Way’s stars.
But by incorporating data from the Gaia observatory, the UofT team was able to obtain a much more comprehensive data set and narrow the distance to galactic center by a significant amount. And this was based on only the initial data released by the Gaia mission. Looking ahead, Hunt anticipates that further data releases will allow his team and other astronomers to refine their calculations even more.
“Gaia’s final release in late 2017 should enable us to increase the precision of our measurement of the Sun’s velocity to within approximately one km/sec,” he said, “which in turn will significantly increase the accuracy of our measurement of our distance from the Galactic center.”
As more next-generation space telescopes and observatories are deployed, we can expect them to provide us with a wealth of new information about our Universe. And from this, we can expect that astronomers and astrophysicists will begin to shine the light on a number of unresolved cosmological questions.