Artist's Concept of Milky Way vs Galaxy MACS2129-1. Credit: hubblesite.org
Thanks to recent improvements in space-based and ground-based telescopes, astronomers have been able to probe deeper into the Universe than ever before. By looking billions of years back in time, we are able to test our theories about the history of galactic formation and evolution. Unfortunately, studying the very early Universe is a daunting task, and one that is beyond the capabilities of our current instruments.
But by combining the power of the Hubble Space Telescope with a technique known as gravitational lensing, a team of astronomers made the first discovery of a compact galaxy that stopped making stars just a few billion years after the Big Bang. The discovery of such a galaxy existing so early in the Universe is unprecedented and represents a major challenge to \theories of how massive galaxies form and evolve.
Their findings were reported in a study titled “A Massive, Dead Disk Galaxy in the Early Universe“, which appeared in the June 22 issue of the journal Nature. As is indicated in the study, the team relied on data from Hubble which they combined with gravitational lensing – where a massive cluster of galaxies magnifies and stretches images of more distant galaxies beyond them – to study the distant galaxy known as MACS 2129-1.
Image of the Galaxy Cluster MACS J2129-0741, as part of CLASH. Credit: hubblesite.org
What they found was completely unexpected. Given the age of the galaxy – dated to just three billion years after the Big Bang – they expected to see a chaotic ball of stars that were forming due to early galaxies merging. Instead, they noticed that the galaxy, which was disk-shaped (like the Milky Way), was effectively dead – meaning that star formation had already ceased within it.
This was a surprise, seeing as how astronomers did not expect to see this so early in the Universe. What’s more, it was the first time that direct evidence has been obtained that shows how at least some of the earliest “dead” galaxies in the Universe evolved from disk-shaped objects to become the giant elliptical galaxies that we regularly see in the Universe today.
As Sune Toft – a researcher from the Dark Cosmology Center at the Niels Bohr Institute and the lead author on the study – explained, this may force a rethink of how galaxies evolved in the early Universe:
“This new insight may force us to rethink the whole cosmological context of how galaxies burn out early on and evolve into local elliptical-shaped galaxies, Perhaps we have been blind to the fact that early “dead” galaxies could in fact be disks, simply because we haven’t been able to resolve them.”
In previous studies, it was assumed that distant dead galaxies were similar in structure to the local elliptical galaxies they eventually evolved into. Prior to this study, confirmation of this hypothesis was not possible since current instruments are not powerful enough to see that far into space. But by combining the power of gravitational lensing with Hubble’s high resolution, Toft and his team were able to see this dead galaxy clearly.
Galaxy Cluster MACS J2129-0741 and Lensed Galaxy MACS2129- Credit: hubblesite.org
Combining rotational velocity measurements from the ESO’s Very Large Telescope (VLT) with archival data from the Cluster Lensing And Supernova survey with Hubble (CLASH), they were able to determine the size of the galaxy, mass, and age as well as its (defunct) rate of star formation. Ultimately, they found that the remote galaxy is three times as massive as the Milky Way, though only half its size, and is spinning more than twice as fast.
Why this galaxy stopped forming stars is still unknown, and will require follow-up surveys using more sophisticated instruments. But in the meantime, there are some possible theories. For instance, it could be the result of an active galactic nucleus, where a supermassive black hole at the center of MACS 2129-1 inhibited star formation by heating the galaxy’s gas and expelling it from the galaxy.
Or it may be the result of cold gas being streamed into the galaxy’s center where it was rapidly heated and compressed, thereby preventing it from cooling and forming star-forming clouds. But when it comes to how these types of early, dead galaxies could have led to the elliptical galaxies we see today, Toft and his colleagues think they know the answer. As he explained, it could be through mergers:
“If these galaxies grow through merging with minor companions, and these minor companions come in large numbers and from all sorts of different angles onto the galaxy, this would eventually randomize the orbits of stars in the galaxies. You could also imagine major mergers. This would definitely also destroy the ordered motion of the stars.”
In the coming years, Toft and his team hope to take advantage of the James Webb Telescope (which will be launching in 2018) to search for more early dead galaxies, in the hopes that it can shed light on the unresolved questions this discover raises. And with the ability to probe deeper into space, astronomers anticipate that a great deal more will be revealed about the early Universe.
Artist's impression of two merging black holes. Credit: Bohn, Throwe, Hébert, Henriksson, Bunandar, Taylor, Scheel/SXS
The discovery of gravitational waves by the LIGO experiment in 2015 sent ripples through the scientific community. Originally predicted by Einstein’s Theory of General Relativity, the confirmation of these waves (and two subsequent detections) solved a long-standing cosmological mystery. In addition to bending the fabric of space-time, it is now known that gravity can also create perturbations that can be detected billions of light-years away.
Seeking to capitalize on these discoveries and conduct new and exciting research into gravitational waves, the European Space Agency (ESA) recently green-lighted the Laser Interferometer Space Antenna (LISA) mission. Consisting of three satellites that will measure gravitational waves directly through laser interferometry, this mission will be the first space-based gravitational wave detector.
This decision was announced yesterday (Tuesday, June 20th) during a meeting of ESA’s Science Program Committee (SPC). It’s implementation is part of the ESA’s Cosmic Vision plan – the current cycle of the agency’s long-term planning for space science missions – which began in 2015 and will be running until 2025. It is also in keeping with the ESA’s desire to study the “invisible universe“, a policy that was adopted in 2013.
To accomplish this, the three satellites that make up the LISA constellation will be deployed into orbit around Earth. Once there, they will assume a triangular formation – spaced 2.5 million km (1.55 million mi) apart – and follow Earth’s orbit around the Sun. Here, isolated from all external influences but Earth’s gravity, they will then connect to each other by laser and begin looking for minute perturbations in the fabric of space-time.
Much like how the LIGO experiment and other gravitational wave detectors work, the LISA mission will rely on laser interferometry. This process consists of a beam of electromagnetic energy (in this case, a laser) being split in two and then recombined to look for patterns of interference. In LISA’s case, two satellites play the role of reflectors while the remaining one is the both source of the lasers and the observer of the laser beam.
When a gravitational wave passes through the triangle established by the three satellites, the lengths of the two laser beams will vary due to the space-time distortions caused by the wave. By comparing the laser beam frequency in the return beam to the frequency of the sent beam, LISA will be able to measure the level of distortion.
These measurements will have to be extremely precise, since the distortions they are looking for affect the fabric of space-time on the most minuscule of levels – a few millionths of a millionth of a meter over a distance of a million kilometers. Luckily, the technology to detect these waves has already been tested by the LISA Pathfinder mission, which deployed in 2015 and will conclude its mission at the end of the month.
Artist’s concept of the LISA mission. Credit: AEI/Milde Marketing/Exozet
In the coming weeks and months, the ESA will be looking over the design of the LISA mission and completing a cost assessment. If all goes as planned, the mission will be proposed for “adoption” before construction begins and it is expected to be launched by 2034. In the same meeting, the ESA also adopted another important mission that will be searching for exoplanets in the coming years.
This mission is known as the PLAnetary Transits and Oscillations of stars, or PLATO, mission. Like Kepler, this mission will monitor stars within a large sections of the sky to look for small dips in their brightness, which are caused by planets passing between the star and the observer (i.e. the transit method). Originally selected in February of 2014, this mission is now moving from the blueprint phase into construction and will launch in 2026.
It’s an exciting time for the European Space Agency. In recent years, it has committed itself to multiple endeavors in the hope of maintaining Europe’s commitment to and continued presence in space. These include studying the “invisible universe”, mounting missions to the Moon and Mars, maintaining a commitment to the International Space Station, and even building a successor to the ISS on the Moon!
These two images reveal a moon orbiting the dwarf planet
2007 OR10. NASA/Hubble/ESA/STScI
These two images reveal a moon orbiting the dwarf planet 2007 OR10. NASA/Hubble/ESA/STScI
It isn’t every day we get a new moon added to the list of solar system satellites. The combined observational power of three observatories — Kepler, Herschel and Hubble — led an astronomical detective tale to its climatic conclusion: distant Kuiper Belt Object 2007 OR10has a tiny moon.
The dwarf planet itself is an enigma wrapped in a mystery: with a long orbit taking it out to a distant aphelion 101 astronomical units (AU) from the Sun, back into the environs of Neptune and Pluto for a perihelion 33 AU from the Sun once every 549 years, 2007 OR10 was discovered by Caltech astronomers Megan Schwamb and Mike Brown in 2007. Nicknamed “Snow White” by Mike Brown for its presumed high albedo, 2007 OR10 was 85 AU distant in the constellation Aquarius at the time of discovery and outbound towards aphelion in 2135. 2007 OR10 is about 1,500 kilometers in diameter, the third largest body known beyond Neptune in our solar system next to Pluto and Eris (nee Xena).
See the moon (circled?) at +21st magnitude, it’s a tough catch! NASA/Hubble/STScI
Enter the Kepler Space Telescope, which imaged 2007 OR10 crossing the constellation Aquarius as part of its extended K2 exoplanet survey along the ecliptic plane. Though Kepler looks for transiting exoplanets — worlds around other stars that betray their presence by tiny dips in the brightness of their host as they pass along our line of sight — it also picks up lots of other things that flicker, including variable stars and distant Kuiper Belt Objects. But the slow 45 hour rotational period of 2007 OR10 noted by Kepler immediately grabbed astronomers interest: could an unseen moon be lurking nearby, dragging on the KBO like a car brake?
“Typical rotation periods for Kuiper Belt Objects are under 24 hours,” says Csaba Kiss (Konkoly Observatory) in a recent press release. “We looked in the Hubble archive because the slower rotation period could have been caused by the gravitational tug of a moon.”
And sure enough, digging back through archival data from the Hubble Space Telescope taken during a survey of KBOs, astronomers turned up two images of the faint moon from 2009 and 2010. Infrared observations of 2007 OR10 and its moon by the European Space Agency’s Herschel Space Telescope cinched the discovery, and noted an albedo of 19% (similar to wet sand) for 2007 OR10, much darker than expected. The moon is about 200 miles (320 kilometers) in diameter, in a roughly 9,300 mile (15,000 kilometer) orbit.
The discovery was announced at an AAS meeting just last year, and even now, we’re still puzzling out what little we know about these distant worlds. Just what 2007 OR10 and its moon looks like is any guess. New Horizons gave us our first look at Pluto and Charon two short summers ago in 2015, and will give us a fleeting glimpse of 2014 MU69 on New Year’s Day 2019. All of these objects beg for proper names, especially pre-2019 New Horizons flyby.
This also comes on the heels of two new moons for Jupiter, recently announced last month S/2017 J1 and J2.
What would the skies from the tiny moon look like? Well, ancient 2007 OR10 must loom large in its sky, though Sol would only shine as a bright -15th magnitude star, (a little brighter than a Full Moon) its illumination dimmed down to 1/7,000th the brightness enjoyed here on sunny Earth, which would be lost in its glare.
The current position of 2007 OR10 in the night sky. Stellarium
And looking at the strange elliptical orbits of these outer worldlets, we can only surmise that something else must be out there. Will the discovery of Planet 9 be made before the close of the decade?
One thing’s for sure: this isn’t your parent’s tidy solar system with “Excellent Mothers” serving “Nine Pizzas.”
Artist's impression of rocky exoplanets orbiting Gliese 832, a red dwarf star just 16 light-years from Earth. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org).
The Kepler space telescope is surely the gift that keeps on giving. After being deployed in 2009, it went on to detect a total of 2,335 confirmed exoplanets and 582 multi-planet systems. Even after two of its reaction wheels failed, it carried on with its K2 mission, which has discovered an additional 520 candidates, 148 of which have been confirmed. And with yet another extension, which will last beyond 2018, it shows no signs of stopping!
In the most recent catalog to be released by the Kepler mission, an additional 219 new planet candidates have been added to its database. More significantly, 10 of these planets were found to be terrestrial (i.e. rocky), of comparable in size to Earth and orbited within their star’s habitable zone – the distance where surface temperatures would be warm enough to support liquid water.
These findings were presented at a news conference on Monday, June 19th, at NASA’s Ames Research Center. Of all the catalogs of Kepler candidates that have been released to date, this one is the most comprehensive and detailed. The eighth in a series of Kepler exoplanet catalogs, this one is based on data that was obtained from the first four years of the mission and is the final catalog that covers the spacecraft’s observations of the Cygnus constellation.
Credits: NASA/Wendy Stenzel
Since 2014, Kepler has ceased looking at a set starfield in the Cygnus constellation and has been collecting data on its second mission – observing fields on the plane of the ecliptic of the Milky Way Galaxy. With the release of this catalog, there are now 4,034 planet candidates that have been identified by Kepler – of which 2,335 have been verified.
An important aspect of this catalog were the methods that were used for producing it, which were the most sophisticated to date. As with all planets detected by Kepler, the latest finds were all made using the transit method. This consists of monitoring stars for occasional dips in brightness, which is used to confirm the presence of planets transiting between the star and the observer.
To ensure that the detections in this latest catalog were real, the team relied on two approaches to eliminate false positives. This consisted of introducing simulated transits into the dataset to make sure the dips that Kepler detected were consistent with planets. Then, they added false signals to see how often the analysis mistook these for planet transits. From this, they were able to tell which planets were overcounted and which were undercounted.
This led to another exciting find, which was the indication that for all of the smaller exoplanets discovered by Kepler, most fell within one of two distinct groupings. Essentially, half the planets that we know of in the galaxy are either rocky in nature and larger than Earth (i.e. Super-Earth’s), or are gas giants that are comparable in size to Neptune (i.e. smaller gas giants).
This conclusion was reached by a team of researchers who used the W.M. Keck Observatory to measure the sizes of 1,300 stars in the Kepler field of view. From this, they were able to determine the radii of 2,000 Kepler planets with extreme precision, and found that there was a clear division between rocky, Earth-sized planets and gaseous planets smaller than Neptune – with few in between.
As Benjamin Fulton, a doctoral candidate at the University of Hawaii in Manoa and the lead author of this study, explained:
“We like to think of this study as classifying planets in the same way that biologists identify new species of animals. Finding two distinct groups of exoplanets is like discovering mammals and lizards make up distinct branches of a family tree.”
These results are sure to have drastic implications when it comes to knowing the frequency of different types of planets in our galaxy, as well as the study of planet formation. For instance, they noted that most rocky planets discovered by Kepler are up to 75% larger than Earth. And for reasons that are not yet clear, about half of them take on hydrogen and helium, which swells their size to the point that they become almost Neptune-sized.
Histogram shows the number of planets per 100 stars as a function of planet size relative to Earth. Credits: NASA/Ames Research Center/CalTech/University of Hawaii/B.J. Fulton
These findings could similarly have significant implications in the search for habitable planets and extra-terrestrial life. As Mario Perez, Kepler program scientist in the Astrophysics Division of NASA’s Science Mission Directorate, said during the presentation:
“The Kepler data set is unique, as it is the only one containing a population of these near Earth-analogs – planets with roughly the same size and orbit as Earth. Understanding their frequency in the galaxy will help inform the design of future NASA missions to directly image another Earth.”
From this information, scientists will be able to know with a greater degree of certainty just how many “Earth-like” planets exist within our galaxy. The most recent estimates place the number of planets in the Milky Way at about 100 billion. And based on this data, it would seem that many of these are similar in composition to Earth, albeit larger.
Combined with a statistical models of how many of these can be found within a circumstellar habitable zone, we should have a better idea of just how many potentially-life-bearing worlds are out there. If nothing else, this should simplify some of the math in the Drake Equation!
In the meantime, the Kepler space telescope will continue to make observations of nearby star systems in order to learn more about their exoplanets. This includes the TRAPPIST-1 system and its seven Earth-sized, rocky planets. Its a safe bet that before it is finally retired after 2018, it will have some more surprises in store for us!
The open star clusters of Messier 46 and Messier 47, located in the southern skies in the Puppis constellation. Credit: Wikisky
Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at Orion’s Nebula’s “little brother”, the De Marian’s Nebula!
During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.
One of these objects is the open star cluster known as Messier 47 (NGC 2422), which is located in the constellation of Puppis roughly 1,600 light-years from Earth. Located in proximity to Messier 46, this star cluster is estimated to be 78 million years in age. It is also particularly bright, containing about 50 stars and occupying a region that is about the same size as that of the full Moon.
Description:
Spanning across about 12 light years of space, this clump of around 50 stars began their life around 78 million years ago. Now cruising through space some 1600 light years away from Earth, the group continues to distance itself from our solar system at a speed of 9 kilometers per second. For the most part, Messier 47 is a whole lot like the Pleiades star cluster – its brightest member shining just around magnitude 6 and holding a spectral class B2.
But, here you will also find two orange K giants with luminosity of about 200 times that of the Sun. At M47’s center you’ll find binary star, Sigma 1121, with components of magnitude 7.9 both and separated by 7.4 arc seconds. How do we know that M47 is a lot like the Pleiades? Let’s try X-ray sources and the advances of looking at open clusters far more differently than in optical wavelengths. As M. Barbera (et al) said in a 2002 study:
“We present the results of a ROSAT study of NGC 2422, a southern open cluster at a distance of about 470 pc, with an age close to the Pleiades. Source detection was performed on two observations, a 10-ks PSPC and a 40-ks HRI pointing, with a detection algorithm based on wavelet transforms, particularly suited to detecting faint sources in crowded fields. We have detected 78 sources, 13 of which were detected only with the HRI, and 37 detected only with the PSPC. For each source, we have computed the 0.2-2.0 keV X-ray flux. Using optical data from the literature and our own low-dispersion spectroscopic observations, we find candidate optical counterparts for 62 X-ray sources, with more than 80% of these counterparts being late type stars. The number of sources (38 of 62) with high membership probability counterparts is consistent with that expected for Galactic plane observations at our sensitivity. We have computed maximum likelihood X-ray luminosity functions (XLF) for F and early-G type stars with high membership probability. Heavy data censoring due to our limited sensitivity permits determination of only the high-luminosity tails of the XLFs; the distributions are indistinguishable from those of the nearly coeval Pleiades cluster.”
What else might be hiding inside Messier 47? Try new debris disk candidates. As Nadya Gorlova (et al) indicated in a 2004 study:
“Sixty-three members of the 100 Myr old open cluster M47 (NGC 2422) have been detected with the Spitzer Space Telescope. The Be star V 378 Pup shows an excess both in the near-infrared, probably due to free-free emission from the gaseous envelope. Seven other early-type stars show smaller excesses. Among late-type stars, two show large excesses. P1121 is the first known main-sequence star showing an excess comparable to that of Beta Pic, which may indicate the presence of an exceptionally massive debris disk. It is possible that a major planetesimal collision has occurred in this system, consistent with the few hundred Myr timescales estimated for the clearing of the solar system.”
Iof the star cluster Messier 47 taken by the Wide Field Imager camera on the 2.2-metre telescope at ESO’s La Silla Observatory in Chile. Credit: ESO
History of Observation:
Messier 47 was originally discovered before 1654 by Hodierna who described it as:
“[A] Nebulosa between the two dogs”… but it was an observation that wasn’t known about until long after Charles Messier independently recovered it on February 19, 1771. “Cluster of stars, little distant from the preceding; the stars are greater; the middle of the cluster was compared with the same star, 2 Navis. The cluster contains no nebulosity.”
However, it was one of those very rare circumstances when Messier actually made a mistake in his position calculations. Despite this error, the cluster was observed by Caroline Herschel and identified as M47 at least twice in early 1783.
As a consequence of Messier’s position mistake, Sir William Herschel also independently rediscovered it on February 4, 1785, and gave it the number H VIII.38. “A cluster of pretty compressed large [bright] and small [faint] stars. Round. Above [more than] 15′ diameter.” It would be John Herschel, on December 16, 1827, who would be the first to resolve Sigma 1121: “The chief star of a large, pretty rich, straggling cluster. It [the star] is double.”
Atlas Image mosaic obtained of Messier 47 as part of the Two Micron All Sky Survey (2MASS). Credit: UMass/IPAC/Caltech/NASA/NSF
The “Messy” mistake would haunt star catalogs – including both Herschel’s and Dreyer’s for years, until the whole clerical error was cleared up by Owen Gingerich in 1960:
“More explicit reasons for this identification [of M47 with NGC 2422] were given independently in 1959 by T.F. Morris, a member of the Messier Club of the Royal Astronomical Society of Canada’s Montreal Centre. Dr. Morris suggested that an error in signs in the difference between M47 and the comparison star could account for the position. Messier determined the declination of a nebula or cluster by measuring the difference between the object and a comparison star of known declination. The right ascension could be found by recording the times at which the object and the star drifted across a central wire in his telescope’s field; the time interval gives the difference in right ascension. The differences between Messier’s 1770 [actually 1771] position for M47 and his stated comparison star, 2 Navis (now 2 Puppis), if applied with opposite signs, leads to NGC 2422. Clearly, Messier made a mistake in computation!”
May you have Caroline Herschel’s luck finding it!
Locating Messier 47:
There is no simple way of finding Messier 47 in the finderscope of a telescope, but it’s not too hard with binoculars. Begin your hunt a little more than a fist width east/northeast of bright Sirius (Alpha Canis Majoris)… or about 5 degrees (3 finger widths) south of Alpha Monoceros. (It can sometimes by seen with the unaided eye under good conditions as a dim nebulosity.) There you will find two open clusters that will usually appear in the same average binocular field of view.
Messier 47 location. Image: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)
M47 is the westernmost of the pair. It will appear slightly brighter and the stars will be more fewer and more clearly visible. In the finderscope it will appear as if it is resolving, while neighboring eastern M46 will just look like a foggy patch. Because M47’s stars are brighter, it is better suited to less than perfect sky conditions, showing as a compression that begins to resolve in binoculars and will resolves almost fully even a small telescope.
And here are the quick facts on this Messier Object to help you get started:
Object Name: Messier 47 Alternative Designations: M47, NGC 2422 Object Type: Open Galactic Star Cluster Constellation: Puppis Right Ascension: 07 : 36.6 (h:m) Declination: -14 : 30 (deg:m) Distance: 1.6 (kly) Visual Brightness: 5.2 (mag) Apparent Dimension: 30.0 (arc min)
Just a couple of weeks ago, astronomers from Caltech announced their third detection of gravitational waves from the Laser Interferometer Gravitational-Wave Observatory or LIGO.
As with the previous two detections, astronomers have determined that the waves were generated when two intermediate-mass black holes slammed into each other, sending out ripples of distorted spacetime.
One black hole had 31.2 times the mass of the Sun, while the other had 19.4 solar masses. The two spiraled inward towards each other, until they merged into a single black hole with 48.7 solar masses. And if you do the math, twice the mass of the Sun was converted into gravitational waves as the black holes merged.
On January 4th, 2017, LIGO detected two black holes merging into one. Courtesy Caltech/MIT/LIGO Laboratory
These gravitational waves traveled outward from the colossal collision at the speed of light, stretching and compressing spacetime like a tsunami wave crossing the ocean until they reached Earth, located about 2.9 billion light-years away.
The waves swept past each of the two LIGO facilities, located in different parts of the United States, stretching the length of carefully calibrated laser measurements. And from this, researchers were able to detect the direction, distance and strength of the original merger.
Seriously, if this isn’t one of the coolest things you’ve ever heard, I’m clearly easily impressed.
Now that the third detection has been made, I think it’s safe to say we’re entering a brand new field of gravitational astronomy. In the coming decades, astronomers will use gravitational waves to peer into regions they could never see before.
Being able to perceive gravitational waves is like getting a whole new sense. It’s like having eyes and then suddenly getting the ability to perceive sound.
This whole new science will take decades to unlock, and we’re just getting started.
As Einstein predicted, any mass moving through space generates ripples in spacetime. When you’re just walking along, you’re actually generating tiny ripples. If you can detect these ripples, you can work backwards to figure out what size of mass made the ripples, what direction it was moving, etc.
Even in places that you couldn’t see in any other way. Let me give you a couple of examples.
Black holes, obviously, are the low hanging fruit. When they’re not actively feeding, they’re completely invisible, only detectable by how they gravitational attract objects or bend light from objects passing behind them.
But seen in gravitational waves, they’re like ships moving across the ocean, leaving ripples of distorted spacetime behind them.
With our current capabilities through LIGO, astronomers can only detect the most massive objects moving at a significant portion of the speed of light. A regular black hole merger doesn’t do the trick – there’s not enough mass. Even a supermassive black hole merger isn’t detectable yet because these mergers seem to happen too slowly.
LIGO has already significantly increased the number of black holes with known masses. The observatory has definitively detected two sets of black hole mergers (bright blue). For each event, LIGO determined the individual masses of the black holes before they merged, as well as the mass of the black hole produced by the merger. The black holes shown with a dotted border represent a LIGO candidate event that was too weak to be conclusively claimed as a detection. Credit: LIGO/Caltech/Sonoma State (Aurore Simonnet)
This is why all the detections so far have been intermediate-mass black holes with dozens of times the mass of our Sun. And we can only detect them at the moment that they’re merging together, when they’re generating the most intense gravitational waves.
If we can boost the sensitivity of our gravitational wave detectors, we should be able to spot mergers of less and more massive black holes.
But merging isn’t the only thing they do. Black holes are born when stars with many more times the mass of our Sun collapse in on themselves and explode as supernovae. Some stars, we’ve now learned just implode as black holes, never generating the supernovae, so this process happens entirely hidden from us.
Is there a singularity at the center of a black hole event horizon, or is there something there, some kind of object smaller than a neutron star, but bigger than an infinitely small point? As black holes merge together, we could see beyond the event horizon with gravitational waves, mapping out the invisible region within to get a sense of what’s going on down there.
This illustration shows the merger of two black holes and the gravitational waves that ripple outward as the black holes spiral toward each other. In reality, the area near the black holes would appear highly warped, and the gravitational waves would be difficult to see directly. Credit: LIGO/T. Pyle
We want to know about even less massive objects like neutron stars, which can also form from a supernova explosion. These neutron stars can orbit one another and merge generating some of the most powerful explosions in the Universe: gamma ray bursts. But do neutron stars have surface features? Different densities? Could we detect a wobble in the gravitational waves in the last moments before a merger?
And not everything needs to merge. Sensitive gravitational wave detectors could sense binary objects with a large imbalance, like a black hole or neutron star orbiting around a main sequence star. We could detect future mergers by their gravitational waves.
Are gravitational waves a momentary distortion of spacetime, or do they leave some kind of permanent dent on the Universe that we could trace back? Will we see echoes of gravity from gravitational waves reflecting and refracting through the fabric of the cosmos?
Perhaps the greatest challenge will be using gravitational waves to see beyond the Cosmic Microwave Background Radiation. This region shows us the Universe 380,000 years after the Big Bang, when everything was cool enough for light to move freely through the Universe.
But there was mass there, before that moment. Moving, merging mass that would have generated gravitational waves. As we explained in a previous article, astronomers are working to find the imprint of these gravitational waves on the Cosmic Microwave Background, like an echo, or a shadow. Perhaps there’s a deeper Cosmic Gravitational Background Radiation out there, one which will let us see right to the beginning of time, just moments after the Big Bang.
And as always, there will be the surprises. The discoveries in this new field that nobody ever saw coming. The “that’s funny” moments that take researchers down into whole new fields of discovery, and new insights into how the Universe works.
The Laser Interferometer Gravitational-Wave Observatory (LIGO) facility in Livingston, Louisiana. The other facility is located in Hanford, Washington. Image: LIGO
The LIGO project was begun back in 1994, and the first iteration operated from 2002 to 2012 without a single gravitational wave detection. It was clear that the facility wasn’t sensitive enough, so researchers went back and made massive improvements.
In 2008, they started improving the facility, and in 2015, Advanced LIGO came online with much more sensitivity. With the increased capabilities, Advanced LIGO made its first discovery in 2016, and now two more discoveries have been added.
LIGO can currently only detect the general hemisphere of the sky where a gravitational wave was emitted. And so, LIGO’s next improvement will be to add another facility in India, called INDIGO. In addition to improving the sensitivity of LIGO, this will give astronomers three observations of each event, to precisely detect the origin of the gravitational waves. Then visual astronomers could do follow up observations, to map the event to anything in other wavelengths.
Current operating facilities in the global network include the twin LIGO detectors—in Hanford, Washington, and Livingston, Louisiana—and GEO600 in Germany. The Virgo detector in Italy and the Kamioka Gravitational Wave Detector (KAGRA) in Japan are undergoing upgrades and are expected to begin operations in 2016 and 2018, respectively. A sixth observatory is being planned in India. Having more gravitational-wave observatories around the globe helps scientists pin down the locations and sources of gravitational waves coming from space. Image made in February 2016. Credit: Caltech/MIT/LIGO Lab
A European experiment known as Virgo has been operating for a few years as well, agreeing to collaborate with the LIGO team if any detections are made. So far, the Virgo experiment hasn’t found anything, but it’s being upgraded with 10 times the sensitivity, which should be fully operational by 2018.
A Japanese experiment called the Kamioka Gravitational Wave Detector, or KAGRA, will come online in 2018 as well, and be able to contribute to the observations. It should be capable of detecting binary neutron star mergers out to nearly a billion light-years away.
Just with visual astronomy, there are a set of next generation supergravitational wave telescopes in the works, which should come online in the next few decades.
The Europeans are building the Einstein Telescope, which will have detection arms 10 km long, compared to 4 km for LIGO. That’s like, 6 more km.
There’s the European Space Agency’s space-based Laser Interferometer Space Antenna, or LISA, which could launch in 2030. This will consist of a fleet of 3 spacecraft which will maintain a precise distance of 2.5 million km from each other. Compare that to the Earth-based detection distances, and you can see why the future of observations will come from space.
The Laser Interferometer Space Antenna (LISA) consists of three spacecraft orbiting the sun in a triangular configuration. Credit: NASA
And that last idea, looking right back to the beginning of time could be a possibility with the Big Bang Observer mission, which will have a fleet of 12 spacecraft flying in formation. This is still all in the proposal stage, so no concrete date for if or when they’ll actually fly.
Gravitational wave astronomy is one of the most exciting fields of astronomy. This entirely new sense is pushing out our understanding of the cosmos in entirely new directions, allowing us to see regions we could never even imagine exploring before. I can’t wait to see what happens next.
Alphecca is the brightest star in a C-shaped pattern of stars: the constellation Corona Borealis. It’s near the bright star Arcturus on the sky’s dome. Credit: EarthSky
Welcome to another edition of Constellation Friday! Today, in honor of the late and great Tammy Plotner, we take a look at the “Northern Crown” – the Corona Borealis constellation. Enjoy!
In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of all the then-known 48 constellations. This treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come, effectively becoming astrological and astronomical canon until the early Modern Age.
One of these constellations was Corona Borealis, otherwise known as the “Northern Crown”. This small, faint constellation is the counterpart to Corona Australis – aka. the “Southern Crown”. It is bordered by the constellations of Hercules, Boötes and Serpens Caput, and has gone on to become one of the 88 modern constellations recognized by the International Astronomical Union.
Name and Meaning:
In mythology, Corona Borealis was supposed to represent the crown worn by Ariadne – a present from Dionysus. In Celtic lore, it was known as Caer Arianrhod, or the “Castle of the Silver Circle”, home to the Lady Arianrhod. Oddly enough, it was also known to the Native Americans as well, who referred to it as the “Camp Circle” – a heavenly rendition of their celestial ancestors.
Hercules and Corona Borealis, as depicted in Urania’s Mirror (c.?1825). Credit: Library of Congress
History of Observation:
Corona Borealis was one of the original 48 constellations mentioned in the Almagest by Ptolemy. To the medieval Arab astronomers, the constellation was known as al-Fakkah, which means “separated” or “broken up”– a reference to the resemblance of the constellation’s stars to a loose string of jewels (sometimes portrayed as a broken dish). The name was later Latinized as Alphecca, which was later given to Alpha Coronae Borealis. In 1920, it was adopted by the International Astronomical Union (IAU) as one of the 88 modern constellations.
Notable Objects:
Corona Borealis has no bright stars, 6 main stars and 24 stellar members with Bayer/Flamsteed designations. It’s brightest star – Alpha Coronae Borealis (Alphecca) – is an eclipsing binary located about 75 light years away. The primary components is a white main sequence star that is believed to have a large disc around it (as evidenced by the amount of infrared radiation it emits), and may even have a planetary or proto-planetary system.
The second brightest star, Beta Coronae Borealis (Nusakan), is a spectroscopic binary that is located 114 light years away. It is an Alpha-2 Canum Venaticorum (ACV) type star, a class of variable (named after a star in the constellation Canes Venatici) that are main sequence stars that are chemically peculiar and have strong magnetic fields. Its traditional name, Nusakan, comes from the Arabic an-nasaqan which means “the (two) series.”
Corona Borealis Galaxy Cluster – Abell 2065. Credit: NASA (Wikisky)
Corona Borealis contains few Deep Sky Objects that would be visible to amateur astronomers. The most notable is the Corona Borealis Galaxy Cluster (aka. Abell 2065), a densely-populated cluster located between 1 and 1.5 billion years from Earth. It lies about one degree southwest of Beta Coronae Borealis, in the southwest corner of the constellation. The cluster contains more than 400 galaxies in an area spanning about one degree in the sky.
Corona Borealis also has five stars that have confirmed exoplanets orbiting them, most of which were detected using the radial velocity method. These include the the orange giant Epsilon Coronae Borealis, which has a Super-Jupiter (6.7 Jupiter masses) that orbits it at a distance of 1.3 AU and with a period of 418 days.
There’s also Kappa Coronae Borealis, an orange subgiant that is orbited by both a debris disk and a gas giant. This planet is 2.5 times as massive as Jupiter and orbits the star with a period of 3.4 years. Omicron Coronae Borealis is a clump giant (a type of red giant) with one confirmed exoplanet – a gas giant with 0.83 Jupiter masses that orbits its star every 187 days.
HD 145457 is an orange giant that has one confirmed planet of 2.9 Jupiter masses that takes 176 days to complete an orbit. XO-1 is a yellow main-sequence star located approximately 560 light-years away with a hot Jupiter (roughly the same size as Jupiter) exoplanet. This planet was discovered using the transit method and completes an orbit around its star every three days.
Artist’s concept of “hot Jupiter” orbiting a distant star. Credit: NASA/JPL-Caltech
Finding Corona Borealis:
Corona Borealis is visible at latitudes between +90° and -50° and is best seen at culmination during the month of July. Using binoculars, let’s start with Alpha Coronae Borealis. It’s name is Gemma, or on some star charts – Alphecca. At 75 light years away, we have a nice binary star system whose companion star produces a very faint eclipse every 17.3599 days. Even though Gemma is quite some distance in relative sky terms from Ursa Major, you might be surprised to know that it’s actually part of the Ursa Major moving star group!
Shift your attention to Beta Coronae Borealis. It’s traditional name Nusakan. Again, it looks like one star, but it’s actually two. Nusakan is a double star that’s about 114 light-years and the primary is a variable star that changes every so slightly about every 41 days. The two components are separated by about 0.25 arc seconds – way too close for amateur telescopes – but that’s not all. In 1944 F.J. Neubauer found a small variation in the radial velocity of Nusakan which may lead to a third orbiting body about 10 times the size of Jupiter.
Now have a look at Gamma. Again, we have a binary star that’s just too darn close to split with anything but a large telescope. Struve 1967 is a close binary with an orbit of 91 years. The position angle is 265º and separation about 0.2″. Instead, try focusing your attention on Zeta 1 and Zeta 2. Known as Struve 1965, this pair is a pretty blue white and they are well spaced at 7.03″ and about one stellar magnitude in difference. Nu1 and Nu2 are also very pretty in binoculars. Here we have an optic double star. Although they aren’t physically related, this widely seperated pair of orange giant stars is a pleasing sight in binoculars!
The location of the Corona Borealis Constellation. Credit: IAU/Sky&Telescope magazine
Out of all the singular stars here, you definitely have to take a look at R Coronae Borelis – known as R Cor Bor. Discovered nearly 200 years ago by English amateur, Edward Pigot, R Coronae Borealis is the prototype star of the R Coronae Borealis (RCB) type variables. They are very unusual type of variable star – one where the variability is caused by the formation of a cloud of carbon dust in the line of sight. Near the stellar photosphere, a cloud is formed – dimming the star’s visual brightness by several magnitudes.
Then the cloud dissipates as it moves away from the star. All RCB types are hydrogen-poor, carbon- and helium-rich, and high-luminosity. They are simultaneously eruptive and pulsating. They could fade anywhere from 1 to 9 magnitudes in a month… Or in a hundred days. It’s normally magnitude 6… But it could be magnitude 14. No wonder it has the nickname “Fade-Out star,” or “Reverse Nova”!
Unfortunately, Corona Borealis contains no bright deep sky objects, but it does have one claim to fame – the highly concentrated galaxy cluster, Abell 2065. For observers with larger telescope, many members of this fascinating 1-1.5 billion light years distant group are visible. This rich cluster of galaxies is located slightly more than a degree southwest of Beta Cor Bor and covers about a full degree of sky! Not for the faint of heart… Some of these galaxies list at magnitude 18….
Artist's impression of a brown dwarf orbiting a white dwarf star. Credit: ESO
Death is simply a part of life, and this is no less the case where stars and other astronomical objects are concerned. Sure, the timelines are much, much greater where these are concerned, but the basic rule is the same. Much like all living organism, stars eventually reach old age and become white dwarfs. And some are not even fortunate enough to be born, instead becoming a class of failed stars known as brown dwarfs.
Despite being familiar with these objects, astronomers were certainly not expecting to find examples of both in a single star system! And yet, according to a new study, that is precisely what an international team of astronomers discovered when looked at WD 1202-024. Using data from the Kepler space telescope, they spotted a binary system consisting of a failed star (a brown dwarf) and the remnant of a star (a white dwarf).
Stardust in the Perseus Molecular Cloud, a star-forming region in the Perseus constellation. Credit & Copyright: Lorand Fenyes
For us Earthlings, life under a single Sun is just the way it is. But with the development of modern astronomy, we’ve become aware of the fact that the Universe is filled with binary and even triple star systems. Hence, if life does exist on planets beyond our Solar System, much of it could be accustomed to growing up under two or even three suns. For centuries, astronomers have wondered why this difference exists and how star systems came to be.
Whereas some astronomers argue that individual stars formed and acquired companions over time, others have suggested that systems began with multiple stars and lost their companions over time. According to a new study by a team from UC Berkeley and the Harvard-Smithsonian Center for Astrophysics (CfA), it appears that the Solar System (and other Sun-like stars) may have started out as binary system billions of years ago.
This study, titled “Embedded Binaries and Their Dense Cores“, was recently accepted for publication in the Monthly Notices of the Royal Astronomical Society. In it, Sarah I. Sadavoy – a radio astronomer from the Max Planck Institute for Astronomy and the CfA – and Steven W. Stahler (a theoretical physicist from UC Berkeley) explain how a radio surveys of a star nursery led them to conclude that most Sun-like stars began as binaries.
The dark molecular cloud, Barnard 68, is a stellar nursery that can only be studied using radio astronomy. Credit: FORS Team, 8.2-meter VLT Antu, ESO
For several decades, astronomers have known that stars are born inside “stellar nurseries”, which are the dense cores that exist within immense clouds of dust and cold, molecular hydrogen. These clouds look like holes in the star field when viewed through an optical telescope, thanks to all the dust grains that obscure light coming from the stars forming within them and from background stars.
Radio surveys are the only way to probe these star-forming regions, since the dust grains emit radio transmissions and also do not block them. For years, Stahler has been attempting to get radio astronomers to examine molecular clouds in the hope of gathering information on the formation of young stars inside them. To this end, he approached Sarah Sadavoy – a member of the VANDAM team – and proposed a collaboration.
The two began their work together by conducting new observations of both single and binary stars within the dense core regions of the Perseus cloud. As Sadavoy explained in a Berkeley News press release, the duo were looking for clues as to whether young stars formed as individuals or in pairs:
“The idea that many stars form with a companion has been suggested before, but the question is: how many? Based on our simple model, we say that nearly all stars form with a companion. The Perseus cloud is generally considered a typical low-mass star-forming region, but our model needs to be checked in other clouds.”
Infrared image from the Hubble Space Telescope, showing a bright, fan-shaped object (lower right quadrant) thought to be a binary star that emits light pulses as the two stars interact. Credit: NASA/ESA/ J. Muzerolle (STScI)
Their observations of the Perseus cloud revealed a series of Class 0 and Class I stars – those that are <500,000 old and 500,000 to 1 million years old, respectively – that were surrounded by egg-shaped cocoons. These observations were then combined with the results from VANDAM and other surveys of star forming regions – including the Gould Belt Survey and data gathered by SCUBA-2 instrument on the James Clerk Maxwell Telescope in Hawaii.
From this, they created a census of stars within the Perseus cloud, which included 55 young stars in 24 multiple-star systems (all but five of them binary) and 45 single-star systems. What they observed was that all of the widely separated binary systems – separated by more than 500 AU – were very young systems containing two Class 0 stars that tended to be aligned with the long axis of their egg-shaped dense cores.
Meanwhile, the slightly older Class I binary stars were closer together (separated by about 200 AU) and did not have the same tendency as far as their alignment was concerned. From this, the study’s authors began mathematically modelling multiple scenarios to explain this distribution, and concluded that all stars with masses comparable to our Sun start off as wide Class 0 binaries. They further concluded that 60% of these split up over time while the rest shrink to form tight binaries.
“As the egg contracts, the densest part of the egg will be toward the middle, and that forms two concentrations of density along the middle axis,” said Stahler. “These centers of higher density at some point collapse in on themselves because of their self-gravity to form Class 0 stars. “Within our picture, single low-mass, sunlike stars are not primordial. They are the result of the breakup of binaries. ”
The two brightest stars of the Centaurus constellation, the binary star system of Alpha Centauri. Credit: Wikipedia Commons/Skatebiker
Findings of this nature have never before been seen or tested. They also imply that each dense core within a stellar nursery (i.e. the egg-shaped cocoons, which typically comprise a few solar masses) converts twice as much material into stars as was previously thought. As Stahler remarked:
“The key here is that no one looked before in a systematic way at the relation of real young stars to the clouds that spawn them. Our work is a step forward in understanding both how binaries form and also the role that binaries play in early stellar evolution. We now believe that most stars, which are quite similar to our own sun, form as binaries. I think we have the strongest evidence to date for such an assertion.”
This new data could also be the start of a new trend, where astronomers rely on radio telescopes to examine dense star-forming regions with the hopes of witnessing more in the way of stellar formations. With the recent upgrades to the VLA and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, and the ongoing data provided by the SCUBA-2 survey in Hawaii, these studies may be coming sooner other than later.
Another interesting implication of the study has to do with something known as the “Nemesis hypothesis”. In the past, astronomers have conjectured that a companion star named “Nemesis” existed within our Solar System. This star was so-named because the theory held that it was responsible for kicking the asteroid which caused the extinction of the dinosaurs into Earth’s orbit. Alas, all attempts to find Nemesis ended in failure.
Artist’s impression of the binary star system of Sirius, a white dwarf star in orbit around Sirius (a white supergiant). Credit: NASA, ESA and G. Bacon (STScI)
As Steven Stahler indicated, these findings could be interpreted as a new take on the Nemesis theory:
“We are saying, yes, there probably was a Nemesis, a long time ago. We ran a series of statistical models to see if we could account for the relative populations of young single stars and binaries of all separations in the Perseus molecular cloud, and the only model that could reproduce the data was one in which all stars form initially as wide binaries. These systems then either shrink or break apart within a million years.”
So while their results do not point towards a star being around for the extinction of the dinosaurs, it is possible (and even highly plausible) that billions of years ago, the Solar planets orbited around two stars. One can only imagine what implications this could have for the early history of the Solar System and how it might have affected planetary formation. But that will be the subject of future studies, no doubt!
A new study from the Center for Planetary Science claims that a comet may be responsible fr the famous Wow! Signal. Credit: NASA/JPL-Caltech
On August 15th, 1977, astronomers using the Big Ear radio telescope at Ohio State University detected a 72-second radio signal coming from space. This powerful signal, which quickly earned the nickname the “Wow! signal”, appeared to be coming from the direction of the Sagittarius Constellation, and some went so far as to suggest that it might be extra-terrestrial in origin.
Since then, the Wow! signal has been an ongoing source of controversy among SETI researchers and astronomers. While some have maintained that it is evidence of extra-terrestrial intelligence (ETI), others have sought to find a natural explanation for it. And thanks a team of researchers from the Center of Planetary Science (CPS), a natural explanation may finally have been found.
In the past, possible explanations have ranged from asteroids and exoplanets to stars and even signals from Earth – but these have all been ruled out. And then in 2016, the Center for Planetary Science – a Florida-based non-profit scientific and astronomical organization – proposed a hypothesis arguing that a comet and/or its hydrogen cloud could be the cause.
This was based on the fact that the Wow! signal was transmitting at a frequency of 1,420 MHz, which happens to be the same frequency as hydrogen. This explanation was also appealing because the movement of the comet served as a possible explanation for why the signal has not been detected since. To validate this hypothesis, the CPS team reportedly conducted 200 observations using a 10-meter radio telescope.
This telescope, they claim, was equipped with a spectrometer and a custom feed horn designed to collect a radio signal centered at 1420.25 MHz. Between Nov. 27th, 2016, and Feb. 24th, 2017, they monitored the area of space where the Wow! signal was detected, and found that a pair of Solar comets (which had not been discovered in 1977) happened to conform to their observations, and could therefore have been the source.
Spectra obtained from these comets – P/2008 Y2(Gibbs) and 266/P Christensen – indicated that they were emitting a radio frequency that was consistent with the Wow! signal. As Antonio Paris (a professor at the CPS), described in a recent paper that appeared in the Journal of the Washington Academy of Sciences:
“The investigation discovered that comet 266/P Christensen emitted a radio signal at 1420.25 MHz. All radio emissions detected were within 1° (60 arcminutes) of the known celestial coordinates of the comet as it transited the neighborhood of the ‘Wow!’ Signal. During observations of the comet, a series of experiments determined that known celestial sources at 1420 MHz (i.e., pulsars and/or active galactic nuclei) were not within 15° of comet 266/P Christensen.”
The Wow! signal represented as “6EQUJ5”. Credit: Big Ear Radio Observatory/NAAPO
The team also examined three other comets to see if they emitted similar radio signals. These comets – P/2013 EW90 (Tenagra), P/2016 J1-A (PANSTARRS), and 237P/LINEAR – were selected randomly from the JPL Small Bodies database, and were confirmed to emit a radio signal at 1420 MHz. Therefore, the results of this investigation conclude that the 1977 “Wow!” Signal was a natural phenomenon from a Solar System body.
However, not everyone is convinced. In response to the paper, Yvette Cendes – a PhD student with the Dunlap Institute at the University of Toronto – wrote a lengthy response on reddit as to why it fails to properly address the Wow! signal. For starters, she cites how the research team measured the signal strength in terms of decibels:
“I have never, ever, EVER used dB in a paper, nor have I ever read a paper in radio astronomy that measured signal strength in dB (except perhaps in the context of an instrumentation paper describing the systems of a radio telescope, i.e. not science but engineering.) We use a different unit in astronomy for flux density, the Jansky (Jy), where 1 Jy= ?230 dBm/(m2·Hz). (dB is a log scale, and Janskys are not.)”
Another point of criticism is the lack of detail in the paper, which would make reproducing the results very difficult – a central requirement where scientific research is concerned. Specifically, they do not indicate where the 10-meter radio telescope they used came from – i.e. which observatory of facility it belonged to, or even if it belonged to one at all – and are rather vague about its technical specification.
Spectra obtained from an area in the direction of the Sagittarius constellation. Credit: The Center for Planetary Science
Last, but not least, there is the matter of the environment in which the observations took place, which are not specified. This is also very important for radio astronomy, as it raised the issue of interference. As Cendes put it:
“This might sound pedantic, but this is insanely important in radio astronomy, where most signals we ever search for are a tiny fraction of the man-made ones, which can be millions of times brighter than an astronomical signal. (A cell phone on the moon would be one of the brighter radio astronomy sources in the sky, to give you an idea!) Radio Frequency Interference (RFI) is super important for the field, so much that people can spend their careers on it (I’ve written a chapter on my thesis on this myself), and the “radio environment” of an observatory can be worth a paper in itself.”
Beyond these apparent incongruities, Cendes also states that the hypothesis for the experiment was flawed. Essentially, the Big Ear searched for the same signal for a period of 22 years, but found nothing. If the comet hypothesis held true, there should be an explanation as to why no trace of the signal was found until this time. Alas, one is lacking, as far as this most recent study is concerned.
“And now you likely have an idea on why one-off events are so hard to prove in science,” she claims. “But then, this is really the major reason the Wow! signal is unsolved to this day- without a plausible explanation, [without] additional data, we just will never know.”
Though it may be hard to accept, it is entirely possible that we may never know what the Wow! signal truly was – whether it was a one-off event, a naturally-occurring phenomena, or something else entirely. And if the comet hypothesis should prove to be unverifiable, then that is certainly good news for the SETI enthusiasts!
While the elimination of natural explanations doesn’t prove that things like Wow! signal are proof of alien civilizations, it at least indicates that this possibility cannot be ruled out just yet. And for those hopeful that evidence of intelligent life will be someday found, that’s really the best we can hope for… for now!
