We can’t seem to get enough of Saturn. It’s the most visually distinct object in our Solar System (other than the Sun, of course, but it’s kind of hard to gaze at). The Cassini mission to Saturn wrapped up about a year ago, and since then we’re relying on the venerable Hubble telescope to satisfy our appetite for images of the ringed planet.
Eta Carinae, a double star system located 7,500 light years away in the constellation Carina, has a combined luminosity of more than 5 million Suns – making it one of the brightest stars in the Milky Way galaxy. But 170 years ago, between 1837 and 1858, this star erupted in what appeared to be a massive supernova, temporarily making it the second brightest star in the sky.
Strangely, this blast was not enough to obliterate the star system, which left astronomers wondering what could account for the massive eruption. Thanks to new data, which was the result of some “forensic astronomy” (where leftover light from the explosion was examined after it reflected off of interstellar dust) a team of astronomers now think they have an explanation for what happened.
The studies which describe their findings – titled “Exceptionally fast ejecta seen in light echoes of Eta Carinae’s Great Eruption” and “Light echoes from the plateau in Eta Carinae’s Great Eruption reveal a two-stage shock-powered event” – recently appeared in the Monthly Notices of the Royal Astronomical Society.
Both studies were led by Nathan Smith of the University of Arizona’s Steward Observatory, and included members from the
In their first study, the team indicates how they studied the “light echoes” produced by the explosion, which were reflected off of interstellar dust and are just now visible from Earth. From this, they observed that the eruption resulted in material expanding at speeds that were up to 20 times faster than with any previously-observed supernova.
In the second study, the team studied the evolution of the echo’s light curve, which revealed that it experienced spikes before 1845, then plateaued until 1858 before steadily declining over the next decade. Basically, the observed velocities and light curve were consistent with the blast wave of a supernova explosion rather than the relatively slow and gentle winds expected from massive stars before they die.
The light echoes were first detected in images obtained in 2003 by telescopes at the Cerro Tololo Inter-American Observatory in Chile. For the sake of their study, the team consulted spectroscopic data from the Magellan telescopes at the Las Campanas Observatory and the Gemini South Observatory, both located in Chile. This allowed the team to measure the light and determine the ejecta’s expansion speeds – more than 32 million km/h (20 million mph).
Based on this data, the team hypothesized that the eruption may have been triggered by a prolonged battle between three stars, which destroyed one star and left the other two in a binary system. This battle may have culminated with a violent explosion when Eta Carinae devoured one of its two companions, sending more than 10 Solar masses into space. This ejected mass created the gigantic bipolar nebula (aka. “the Homunculus Nebula”) which is seen today.
As Smith explained in a recent HubbleSite press release:
“We see these really high velocities in a star that seems to have had a powerful explosion, but somehow the star survived. The easiest way to do this is with a shock wave that exits the star and accelerates material to very high speeds.”
In this scenario, Eta Carinae started out as a trinary system, with two massive stars orbiting close to each other and the third orbiting further away. When the most massive of the binary neared the end of its life, it began to expand and then transfer much of its material onto its slightly smaller companion. This caused the smaller star to accumulate just enough energy to cause it to eject its outer layers, but not enough to completely annihilate it.
The companion star would have then grown to become about 100 times the mass of our Sun and extremely bright. The other star, now weighing only 30 Solar masses, would have been stripped of its hydrogen layers, exposing its hot helium core – which represent an advanced stage of evolution in the lives of massive stars. As Armin Rest – a researcher from the explained:
“From stellar evolution, there’s a pretty firm understanding that more massive stars live their lives more quickly and less massive stars have longer lifetimes. So the hot companion star seems to be further along in its evolution, even though it is now a much less massive star than the one it is orbiting. That doesn’t make sense without a transfer of mass.”
This transfer of mass would have altered the gravitational balance of the system, causing the helium-core star to move farther away from its now-massive companion and eventually travel so far that it would interact with the outermost third star. This would cause the third star to move towards the massive star and eventually merge with it, producing an outflow of material.
Initially, the merger caused ejecta that expanded relatively slowly, but as the two stars finally joined together, they produced an explosive event that blasted material off 100 times faster. This material caught up to the slow ejecta, pushing it forward and heating the material until it glowed. This glowing material was the main light source that was viewed by astronomers 170 years ago.
In the end, the smaller helium-core star settled into an elliptical orbit around around its massive counterpart, passing through the star’s outer layers every 5.5 years and generating X-ray shock waves. According to Smith, while this explanation cannot account for everything observed in Eta Carinae, it does explain both the brightening and the fact that the star remains:
“The reason why we suggest that members of a crazy triple system interact with each other is because this is the best explanation for how the present-day companion quickly lost its outer layers before its more massive sibling.”
These studies have provided new clues as to the mystery of how Eta Carinae appeared to explode in a massive supernova, but left behind a massive star and nebula. In addition, a better understanding of the physics behind the Eta Carinae explosion could help astronomers to learn more about the complicated interactions that govern binary and multiple star systems – which are critical to our understanding of the evolution and death of massive stars.
In the 1920s, Edwin Hubble made the groundbreaking discovery that the Universe was in a state of expansion. Originally predicted as a consequence of Einstein’s Theory of General Relativity, measurements of this expansion came to be known as Hubble’s Constant. Today, and with the help of next-generation telescopes – like the aptly-named Hubble Space Telescope (HST) – astronomers have remeasured and revised this law many times.
These measurements confirmed that the rate of expansion has increased over time, though scientists are still unsure why. The latest measurements were conducted by an international team using Hubble, who then compared their results with data obtained by the European Space Agency’s (ESA) Gaia observatory. This has led to the most precise measurements of the Hubble Constant to date, though questions about cosmic acceleration remain.
The study which describes their findings appeared in the July 12th issue of the Astrophysical Journal, titled “Milky Way Cepheid Standards for Measuring Cosmic Distances and Application to Gaia DR2: Implications for the Hubble Constant.” The team behind the study included members from the Space Telescope Science Institute (STScI), the Johns Hopkins University, the National Institute for Astrophysics (INAF), UC Berkeley, Texas A&M University, and the European Southern Observatory (ESO).
Since 2005, Adam Riess – a Nobel Laureate Professor with the Space Telescope Science Institute and the Johns Hopkins University – has been working to refine the Hubble Constant value by streamlining and strengthening the “cosmic distance ladder”. Along with his team, known as Supernova H0 for the Equation of State (SH0ES), they have successfully reduced the uncertainty associated with the rate of cosmic expansion to just 2.2%
To break it down, astronomers have traditionally used the “cosmic distance ladder” to measure distances in the Universe. This consists of relying on distance markers like Cepheid variables in distant galaxies – pulsating stars whose distances can be inferred by comparing their intrinsic brightness with their apparent brightness. These measurements are then compared to the way light from distant galaxies is redshifted to determine how fast the space between galaxies is expanding.
From this, the Hubble Constant is derived. Another method that is used is to observe the Cosmic Microwave Background (CMB) to trace the expansion of the cosmos during the early Universe – circa. 378,000 years after the Big Bang – and then using physics to extrapolate that to the present expansion rate. Together, the measurements should provide an end-to-end measurement of how the Universe has expanded over time.
However, astronomers have known for some time that the two measurements don’t match up. In a previous study, Riess and his team conducted measurements using Hubble to obtain a Hubble Constant value of 73 km/s (45.36 mps) per megaparsec (3.3 million light-years). Meanwhile, results based on the ESA’ Planck observatory (which observed the CMB between 2009 and 2013) predicted that the Hubble constant value should now be 67 km/s (41.63 mps) per megaparsec and no higher than 69 km/s (42.87 mps) – which represents a discrepancy of 9%.
As Riess indicated in a recent NASA press release:
“The tension seems to have grown into a full-blown incompatibility between our views of the early and late time universe. At this point, clearly it’s not simply some gross error in any one measurement. It’s as though you predicted how tall a child would become from a growth chart and then found the adult he or she became greatly exceeded the prediction. We are very perplexed.”
In this case, Riess and his colleagues used Hubble to gauge the brightness of distant Cepheid variables while Gaia provided the parallax information – the apparent change in an objects position based on different points of view – needed to determine the distance. Gaia also added to the study by measuring the distance to 50 Cepheid variables in the Milky Way, which were combined with brightness measurements from Hubble.
This allowed the astronomers to more accurately calibrate the Cepheids and then use those seen outside the Milky Way as milepost markers. Using both the Hubble measurements and newly released data from Gaia, Riess and his colleagues were able to refine their measurements on the present rate of expansion to 73.5 kilometers (45.6 miles) per second per megaparsec.
As Stefano Casertano, of the Space Telescope Science Institute and a member of the SHOES team, added:
“Hubble is really amazing as a general-purpose observatory, but Gaia is the new gold standard for calibrating distance. It is purpose-built for measuring parallax—this is what it was designed to do. Gaia brings a new ability to recalibrate all past distance measures, and it seems to confirm our previous work. We get the same answer for the Hubble constant if we replace all previous calibrations of the distance ladder with just the Gaia parallaxes. It’s a crosscheck between two very powerful and precise observatories.”
Looking to the future, Riess and his team hope to continue to work with Gaia so they can reduce the uncertainty associated with the value of the Hubble Constant to just 1% by the early 2020s. In the meantime, the discrepancy between modern rates of expansion and those based on the CMB will continue to be a puzzle to astronomers.
In the end, this may be an indication that other physics are at work in our Universe, that dark matter interacts with normal matter in a way that is different than what scientists suspect, or that dark energy could be even more exotic than previously thought. Whatever the cause, it is clear the Universe still has some surprises in store for us!
Further Reading: NASA
The Hubble Space Telescope is the oldest space telescope in operation, having spent the past twenty-eight years in orbit. Nevertheless, this mission is still hard at work revealing things about our Solar System, neighboring exoplanets, and some of the farthest reaches of the Universe. And every so often, it also captures an image that happens to turn up something interesting and unexpected.
Recently, while conducting a study of Abell 370, a galaxy cluster located approximately four billion light-years away in the constellation Cetus (the Sea Monster), Hubble managed to spot something in foreground. While observing this collection of several hundred galaxiess, the image was photobombed by 22 asteroids whose tails created streaks that looked like background astronomical phenomena.
The study was part of the Frontier Fields program, where Hubble has captured images of some of the earliest galaxies in the Universe (aka. “relic galaxies”) in order to determine how it evolved over time. The position of this asteroid field is near the ecliptic (the plane of our Solar System) where most asteroids reside, which is why Hubble astronomers saw so many crossings.
In the past, Hubble has recorded many instances of asteroid trails when conducting observations along a line-of-sight near the plane of our Solar System. In this case, the Near-Earth Asteroids (NEAs) – which orbit Earth at an average distance of about 260 million km (161.5 million mi) – were previously undetected due to their faintness. But thanks to the images taken by Hubble, scientists were able to identify them manually based on their motion.
Of the 22 asteroids, five were identified as unique objects. The image was assembled from several exposures taken in visible and infrared light, which was first released on November 6th, 2017. The image was prepared in honor of “Asteroid Day”, a global annual event that takes place every June 30th to raise awareness about asteroids and what can be done to protect Earth from a possible impact.
The day falls on the anniversary of the Tunguska event, which took place on June 30th, 1918, in eastern Russia and resulted in the flattening of 2,000 square km (770 square mi) of forest. While far less harmful than the Cretaceous–Paleogene (K–Pg) extinction event – which took place 66 million years ago and is believed to have killed the dinosaurs – Tunguska was the most harmful asteroid event in recorded history.
In many of the images snapped by Hubble, the asteroid tails appeared as white trails that look like curved streaks, an effect caused by parallax. In astronomy, parallax is an observational effect where the apparent position of an object appears to be different based on different lines of sight. Basically, as Hubble orbited around the Earth and took several images of the galaxy, the asteroids appeared to be moving relative to the background stars and galaxies.
The asteroids own motion along their orbits and other contributing factors also led to their streaked appearance. Whereas the white streaks were identified as asteroid tails, the blue streaks are distorted images of distant galaxies behind the cluster. This effect is known as gravitational lensing, where light from distant objects is warped and magnified by the presence of an intervening object.
In this case, the intervening object who’s gravitational force magnified the light of the background galaxies was Abell 370. These more distant galaxies are too distant for Hubble to see directly, hence why astronomers use the technique to study the most distant objects in the Universe. But whereas the blue streaks were expected, the white streaks caused by asteroids took scientists completely by surprise!
This year, the European Space Agency (ESA) is co-hosting a live webcast with the European Southern Observatory (ESO) with expert interviews, news on some the most recent asteroid research, and a discussion about what killed the dinosaurs. You can watch this event tomorrow starting at 13:00 CEST (11:00 UST/04:00 PST) by going to the ESA’s Asteroid Day web page.
Further Reading: ESA
In 1990, the Hubble Space Telescope was placed into Low Earth Orbit. Since then, Hubble has gone on to become the most well-known space observatory and has revealed some never-before-seen things about our Universe. Despite the subsequent deployment of several flagship telescopes – like the Kepler Space Telescope, the Chandra X-ray Observatory and the Spitzer Space Telescope – Hubble is still accomplishing some amazing feats.
For instance, a team of astronomers recently used Hubble to locate the most distant star ever discovered. This hot blue star, which was located in a galaxy cluster, existed just 4.4 billion years after the Big Bang. The discovery of this star is expected to provide new insights into the formation and evolution of stars and galaxy clusters during the early Universe, as well as the nature of dark matter itself.
The discovery was made by an international team of scientists led by Patrick Kelly (of the University of Minnesota), Jose Diego (of the Instituto de Física de Cantabria in Spain) and Steven Rodney (of the University of South Carolina). Together, they observed the distant star in the galaxy cluster MACS J1149-2223 in April 2016 while studying the supernova explosion known as heic1525 (aka. Refsdal).
Using a technique known as gravitational microlensing, team relied on the total mass of the galaxy cluster itself to magnify the light coming from the supernova. However, while looking for this supernova, the team found an unexpected point source of light in the same galaxy. As Patrick Kelly explained in a recent Hubble press release:
“Like the Refsdal supernova explosion the light of this distant star got magnified, making it visible for Hubble. This star is at least 100 times farther away than the next individual star we can study, except for supernova explosions.”
The light observed from this star – named Lensed Star 1 (LS1) – was emitted just 4.4 billion years after the Big Bang (when the Universe was just 30% of its current age). The light was only detectable thanks to the microlensing effect caused by mass of the galaxy cluster and a compact object about three times the mass of our Sun within the galaxy itself. This allowed for the light coming from the star to be magnified by a factor of 2000.
Interestingly enough, the team also realized that this was not the first time this star had been observed. During a previous observation of the galaxy cluster, made in October 2016, the star was also acquired in an image – but went unnoticed at the time. As Diego noted:
“We were actually surprised to not have seen this second image in earlier observations, as also the galaxy the star is located in can be seen twice. We assume that the light from the second image has been deflected by another moving massive object for a long time — basically hiding the image from us. And only when the massive object moved out of the line of sight the second image of the star became visible.”
After finding the star in their survey, the team used Hubble again to obtain spectra from LS1 and determined that it is a B-type supergiant star – an extremely bright and blue class of star that has several times the mass of our Sun and is more than twice as hot. Given the star’s age, the discovery of LS1 is find on its own. At the same time, the discovery of this star will allow astronomers to gain new insights into the galaxy cluster itself.
As Steven Rodney indicated, “We know that the microlensing was caused by either a star, a neutron star, or a stellar-mass black hole.” As such, the discovery of LS1 will allow astronomers to study these objects (the latter of which are invisible) and estimate how many of them exist within this galaxy cluster.
Learning more about the constituents of galaxy clusters – the largest and most massive structures in the Universe – will also provide important clues about the composition of the Universe overall and how it evolved over time. This includes the important role played by dark matter in the evolution the Universe. As Kelly explained:
“If dark matter is at least partially made up of comparatively low-mass black holes, as it was recently proposed, we should be able to see this in the light curve of LS1. Our observations do not favour the possibility that a high fraction of dark matter is made of these primordial black holes with about 30 times the mass of the Sun.”
With the deployment of next-generation telescopes – like the James Webb Space Telescope – astronomers hope to learn even more about the earliest stars in the Universe. In so doing, they will be able to learn more about how it evolved over the past 10 billion years or so, and gain vital clues as to how dark matter played a role. In the meantime, Hubble still plays an all-important role in expanding our understanding of the cosmos.
And be sure to enjoy this episode of Hubblecast that explains this impressive find, courtesy of the ESA:
Further Reading: Hubble Space Telescope
Younger stars have a cloud of dusty debris encircling them, called a circumstellar disk. This disk is material left over from the star’s formation, and it’s out of this material that planets form. But scientists using the Hubble have been studying an enormous dust structure some 150 billion miles across. Called an exo-ring, this newly imaged structure is much larger than a circumstellar disk, and the vast structure envelops the young star HR 4796A and its inner circumstellar disk.
Discovering a dust structure around a young star is not new, and the star in this new paper from Glenn Schneider of the University of Arizona is probably our most (and best) studied exoplanetary debris system. But Schneider’s paper, along with capturing this new enormous dust structure, seems to have uncovered some of the interplay between the bodies in the system that has previously been hidden.
Schneider used the Space Telescope Imaging Spectrograph (STIS) on the Hubble to study the system. The system’s inner disk was already well-known, but studying the larger structure has revealed more complexity.
The origin of this vast structure of dusty debris is likely collisions between newly forming planets within the smaller inner ring. Outward pressure from the star HR 4769A then propelled the dust outward into space. The star is 23 times more luminous than our Sun, so it has the necessary energy to send the dust such a great distance.
A press release from NASA describes this vast exo-ring structure as a “donut-shaped inner tube that got hit by a truck.” It extends much further in one direction than the other, and looks squashed on one side. The paper presents a couple possible causes for this asymmetric extension.
It could be a bow wave caused by the host star travelling through the interstellar medium. Or it could be under the gravitational influence of the star’s binary companion (HR 4796B), a red dwarf star located 54 billion miles from the primary star.
“The dust distribution is a telltale sign of how dynamically interactive the inner system containing the ring is'” – Glenn Schneider, University of Arizona, Tucson.
The asymmetrical nature of the vast exo-structure points to complex interactions between all of the stars and planets in the system. We’re accustomed to seeing the radiation pressure from the host star shape the gas and dust in a circumstellar disk, but this study presents us with a new level of complexity to account for. And studying this system may open a new window into how solar systems form over time.
“We cannot treat exoplanetary debris systems as simply being in isolation. Environmental effects, such as interactions with the interstellar medium and forces due to stellar companions, may have long-term implications for the evolution of such systems. The gross asymmetries of the outer dust field are telling us there are a lot of forces in play (beyond just host-star radiation pressure) that are moving the material around. We’ve seen effects like this in a few other systems, but here’s a case where we see a bunch of things going on at once,” Schneider further explained.
The paper suggests that the location and brightness of smaller rings within the larger dust structure places constraints on the masses and orbits of planets within the system, even when the planets themselves can’t be seen. But that will require more work to determine with any specificity.
This paper represents a refinement and advancement of the Hubble’s imaging capabilities. The paper’s author is hopeful that the same methods using in this study can be used on other similar systems to better understand these larger dust structures, how they form, and what role they play.
As he says in the paper’s conclusion, “With many, if not most, technical challenges now understood and addressed, this capability should be used to its fullest, prior to the end of the HST mission, to establish a legacy of the most robust images of high-priority exoplanetary debris systems as an enabling foundation for future investigations in exoplanetary systems science.”
In the 1920s, Edwin Hubble made the groundbreaking revelation that the Universe was in a state of expansion. Originally predicted as a consequence of Einstein’s Theory of General Relativity, this confirmation led to what came to be known as Hubble’s Constant. In the ensuring decades, and thanks to the deployment of next-generation telescopes – like the aptly-named Hubble Space Telescope (HST) – scientists have been forced to revise this law.
In short, in the past few decades, the ability to see farther into space (and deeper into time) has allowed astronomers to make more accurate measurements about how rapidly the early Universe expanded. And thanks to a new survey performed using Hubble, an international team of astronomers has been able to conduct the most precise measurements of the expansion rate of the Universe to date.
This survey was conducted by the Supernova H0 for the Equation of State (SH0ES) team, an international group of astronomers that has been on a quest to refine the accuracy of the Hubble Constant since 2005. The group is led by Adam Reiss of the Space Telescope Science Institute (STScI) and Johns Hopkins University, and includes members from the American Museum of Natural History, the Neils Bohr Institute, the National Optical Astronomy Observatory, and many prestigious universities and research institutions.
The study which describes their findings recently appeared in The Astrophysical Journal under the title “Type Ia Supernova Distances at Redshift >1.5 from the Hubble Space Telescope Multi-cycle Treasury Programs: The Early Expansion Rate“. For the sake of their study, and consistent with their long term goals, the team sought to construct a new and more accurate “distance ladder”.
This tool is how astronomers have traditionally measured distances in the Universe, which consists of relying on distance markers like Cepheid variables – pulsating stars whose distances can be inferred by comparing their intrinsic brightness with their apparent brightness. These measurements are then compared to the way light from distance galaxies is redshifted to determine how fast the space between galaxies is expanding.
From this, the Hubble Constant is derived. To build their distant ladder, Riess and his team conducted parallax measurements using Hubble’s Wide Field Camera 3 (WFC3) of eight newly-analyzed Cepheid variable stars in the Milky Way. These stars are about 10 times farther away than any studied previously – between 6,000 and 12,000 light-year from Earth – and pulsate at longer intervals.
To ensure accuracy that would account for the wobbles of these stars, the team also developed a new method where Hubble would measure a star’s position a thousand times a minute every six months for four years. The team then compared the brightness of these eight stars with more distant Cepheids to ensure that they could calculate the distances to other galaxies with more precision.
Using the new technique, Hubble was able to capture the change in position of these stars relative to others, which simplified things immensely. As Riess explained in a NASA press release:
“This method allows for repeated opportunities to measure the extremely tiny displacements due to parallax. You’re measuring the separation between two stars, not just in one place on the camera, but over and over thousands of times, reducing the errors in measurement.”
Compared to previous surveys, the team was able to extend the number of stars analyzed to distances up to 10 times farther. However, their results also contradicted those obtained by the European Space Agency’s (ESA) Planck satellite, which has been measuring the Cosmic Microwave Background (CMB) – the leftover radiation created by the Big Bang – since it was deployed in 2009.
By mapping the CMB, Planck has been able to trace the expansion of the cosmos during the early Universe – circa. 378,000 years after the Big Bang. Planck’s result predicted that the Hubble constant value should now be 67 kilometers per second per megaparsec (3.3 million light-years), and could be no higher than 69 kilometers per second per megaparsec.
Based on their sruvey, Riess’s team obtained a value of 73 kilometers per second per megaparsec, a discrepancy of 9%. Essentially, their results indicate that galaxies are moving at a faster rate than that implied by observations of the early Universe. Because the Hubble data was so precise, astronomers cannot dismiss the gap between the two results as errors in any single measurement or method. As Reiss explained:
“The community is really grappling with understanding the meaning of this discrepancy… Both results have been tested multiple ways, so barring a series of unrelated mistakes. it is increasingly likely that this is not a bug but a feature of the universe.”
These latest results therefore suggest that some previously unknown force or some new physics might be at work in the Universe. In terms of explanations, Reiss and his team have offered three possibilities, all of which have to do with the 95% of the Universe that we cannot see (i.e. dark matter and dark energy). In 2011, Reiss and two other scientists were awarded the Nobel Prize in Physics for their 1998 discovery that the Universe was in an accelerated rate of expansion.
Consistent with that, they suggest that Dark Energy could be pushing galaxies apart with increasing strength. Another possibility is that there is an undiscovered subatomic particle out there that is similar to a neutrino, but interacts with normal matter by gravity instead of subatomic forces. These “sterile neutrinos” would travel at close to the speed of light and could collectively be known as “dark radiation”.
Any of these possibilities would mean that the contents of the early Universe were different, thus forcing a rethink of our cosmological models. At present, Riess and colleagues don’t have any answers, but plan to continue fine-tuning their measurements. So far, the SHoES team has decreased the uncertainty of the Hubble Constant to 2.3%.
This is in keeping with one of the central goals of the Hubble Space Telescope, which was to help reduce the uncertainty value in Hubble’s Constant, for which estimates once varied by a factor of 2.
So while this discrepancy opens the door to new and challenging questions, it also reduces our uncertainty substantially when it comes to measuring the Universe. Ultimately, this will improve our understanding of how the Universe evolved after it was created in a fiery cataclysm 13.8 billion years ago.
Back in the late 1980’s, Voyager 2 was the first spacecraft to capture images of the giant storms in Neptune’s atmosphere. Before then, little was known about the deep winds cycling through Neptune’s atmosphere. But Hubble has been turning its sharp eye towards Neptune over the years to study these storms, and over the past couple of years, it’s watched one enormous storm petering out of existence.
“It looks like we’re capturing the demise of this dark vortex, and it’s different from what well-known studies led us to expect.” – Michael H. Wong, University of California at Berkeley.
When we think of storms on the other planets in our Solar System, we automatically think of Jupiter. Jupiter’s Great Red Spot is a fixture in our Solar System, and has lasted 200 years or more. But the storms on Neptune are different: they’re transient.
The storm on Neptune moves in an anti-cyclonic direction, and if it were on Earth, it would span from Boston to Portugal. Neptune has a much deeper atmosphere than Earth—in fact it’s all atmosphere—and this storm brings up material from deep inside. This gives scientists a chance to study the depths of Neptune’s atmosphere without sending a spacecraft there.
The first question facing scientists is ‘What is the storm made of?’ The best candidate is a chemical called hydrogen sulfide (H2S). H2S is a toxic chemical that stinks like rotten eggs. But particles of H2S are not actually dark, they’re reflective. Joshua Tollefson from the University of California at Berkeley, explains: “The particles themselves are still highly reflective; they are just slightly darker than the particles in the surrounding atmosphere.”
“We have no evidence of how these vortices are formed or how fast they rotate.” – Agustín Sánchez-Lavega, University of the Basque Country in Spain.
But beyond guessing what chemical the spot might me made of, scientists don’t know much else. “We have no evidence of how these vortices are formed or how fast they rotate,” said Agustín Sánchez-Lavega from the University of the Basque Country in Spain. “It is most likely that they arise from an instability in the sheared eastward and westward winds.”
There’ve been predictions about how storms on Neptune should behave, based on work done in the past. The expectation was that storms like this would drift toward the equator, then break up in a burst of activity. But this dark storm is on its own path, and is defying expectations.
“We thought that once the vortex got too close to the equator, it would break up and perhaps create a spectacular outburst of cloud activity.” – Michael H. Wong, University of California at Berkeley.
“It looks like we’re capturing the demise of this dark vortex, and it’s different from what well-known studies led us to expect,” said Michael H. Wong of the University of California at Berkeley, referring to work by Ray LeBeau (now at St. Louis University) and Tim Dowling’s team at the University of Louisville. “Their dynamical simulations said that anticyclones under Neptune’s wind shear would probably drift toward the equator. We thought that once the vortex got too close to the equator, it would break up and perhaps create a spectacular outburst of cloud activity.”
Rather than going out in some kind of notable burst of activity, this storm is just fading away. And it’s also not drifting toward the equator as expected, but is making its way toward the south pole. Again, the inevitable comparison is with Jupiter’s Great Red Spot (GRS).
The GRS is held in place by the prominent storm bands in Jupiter’s atmosphere. And those bands move in alternating directions, constraining the movement of the GRS. Neptune doesn’t have those bands, so it’s thought that storms on Neptune would tend to drift to the equator, rather than toward the south pole.
This isn’t the first time that Hubble has been keeping an eye on Neptune’s storms. The Space Telescope has also looked at storms on Neptune in 1994 and 1996. The video below tells the story of Hubble’s storm watching mission.
The images of Neptune’s storms are from the Hubble Outer Planets Atmosphere Legacy (OPAL) program. OPAL gathers long-term baseline images of the outer planets to help us understand the evolution and atmospheres of the gas giants. Images of Jupiter, Saturn, Uranus and Neptune are being taken with a variety of filters to form a kind of time-lapse database of atmospheric activity on the four gas planets.
In 2012, the Hubble Space Telescope Frontier Fields program (aka. Hubble Deep Fields Initiative 2012) officially kicked off. The purpose of this project was to study the faintest and most distant galaxies in the Universe using the gravitational lensing technique, thus advancing our knowledge of early galaxy formation. By 2017, the Frontier Field program wrapped up, and the hard work of analyzing all the data it collected began.
One of the more interesting finds within the Frontier Fields data has been the discovery of low mass galaxies with high star formation rates. After examining the “parallel fields” for Abell 2744 and MACS J0416.1-2403 – two galaxy clusters studied by the program – a pair of astronomers noted the presence of what they refer to as “Little Blue Dots” (LBDs), a finding which has implications for galaxy formation and globular clusters.
The study which details their findings recently appeared online under the title “Little Blue Dots in the Hubble Space Telescope Frontier Fields: Precursors to Globular Clusters?“. The study team consisted of Dr. Debra Meloy Elmegreen – a professor of astronomy at Vassar College – and Dr. Bruce G. Elmegreen, an astronomer with the IBM Research Division at the T.J. Watson Research Center in Yorktown Heights.
To put it simply, the Frontier Fields program used the Hubble Space Telescope to observe six massive galaxy clusters at optical and near-infrared wavelengths – with its Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3), respectively. These massive galaxies were used to magnify and stretch images of remote galaxies located behind them which were otherwise too faint for Hubble to see directly (aka. gravitational lensing).
While one of these Hubble cameras would look at a galaxy cluster, the other would simultaneously view an adjacent patch of sky. These adjacent patches are known as “parallel fields”, otherwise faint regions that provide some of the deepest looks into the early Universe. As Dr. Bruce Elmegreen told Universe Today via email:
“The purpose of the HFF program is to take deep images of 6 regions of the sky where there are clusters of galaxies, because these clusters magnify background galaxies through the gravitational lens effect. In this way, we can see further than just with direct imaging of the sky alone. Many galaxies have been studied using this magnification technique. The clusters of galaxies are important because they are big mass concentrations which make strong gravitational lenses.”
This six galaxy clusters used for the sake of the project included Abell 2744, MACS J0416.1-2403 and their parallel fields, the latter of which were the focal point in this study. These and the other clusters were used to find galaxies that existed just 600 to 900 million years after the Big Bang. These galaxies and their respective parallels had already been cataloged using computer algorithms that automatically found galaxies in the images and determined their properties.
As the research duo go on to explain in their study, recent large-scale deep surveys have enabled studies of smaller galaxies at higher redshifts. These include “green peas” – luminous, compact and low mass galaxies with high specific star formation rates – and even lower-mass “blueberries”, small starburst galaxies that are a faint extension of the green peas that also show intense rates of star formation.
Using the aforementioned catalogues, and examining the parallel fields for Abell 2744 and MACS J0416.1-2403, the team went looking for other examples of low-mass galaxies with high star formation rates. The purpose of this was to measure the properties of these dwarf galaxies, and to see if any of their positions accorded with where globular clusters are known to have formed.
What they found was what they referred to as “Little Blue Dots” (LBSs), which are even lower-mass versions of “blueberries”. As Dr. Debra Elmegreen told Universe Today via email:
“When I was examining the images (there are about 3400 galaxies detected in each field), I noticed occasional galaxies that appeared as little blue dots, which was very intriguing because of Bruce’s previous theoretical work on dwarf galaxies. The published catalogs included redshifts and star formation rates and masses for each galaxy, and it turns out the little blue dots are low mass galaxies with very high star formation rates for their mass.”
These galaxies didn’t show structure, so Debra and Bruce stacked the images of galaxies into 3 different ranges of redshift (which worked out to about 20 galaxies each) to create deeper images. “Still they showed no structure or faint extended outer disk,” said Debra, “so they are at the limit of resolution, with average sizes of 100-200 parsecs (about 300-600 light years) and masses of a few million times the mass of our sun.”
In the end, they determined that within these LBDs, star formation rates were very high. They also noted that these dwarf galaxies were very young, being less than 1% the age of the Universe at the time that they were observed. “So the tiny galaxies just formed,: said Bruce, “and their star formation rates are high enough to account for the globular clusters, maybe one in each LBD, when the star bursts in them wind down after a few tens of million years.”
Debra and Bruce Elmegreen are no strangers to high redshift galaxies. Back in 2012, Bruce published a paper that suggested that the globular clusters that orbit the Milky Way (and most other galaxies) formed in dwarf galaxies during the early Universe. These dwarf galaxies would have since been acquired by larger galaxies like our own, and the clusters are essentially their remnants.
Globular clusters are essentially massive star clusters that orbit around the Milky Way Halo. They are typically around 1 million Solar masses and are made up of stars that are very old – somewhere on the order of 10 to 13 billion years. Beyond the Milky Way, many appear in common orbits and in the Andromeda Galaxy, some even appear connected by a stream of stars.
As Bruce explained, his is a compelling argument for the theory that globular clusters formed from dwarf galaxies in the early Universe:
“This suggests that the metal-poor globular clusters are the dense remnants of little galaxies that got captured by bigger galaxies, like the Milky Way, and ripped apart by tidal forces. This idea for the origin of halo globular clusters goes back several decades… It would be only the metal-poor one that are like this, which are about half the total, because dwarf galaxies are metal poor compared to big galaxies, and they were also more metal poor in the early universe.”
This study has many implications for our understanding of how the Universe evolved, which was the chief aim of the Hubble Frontier Fields program. By examining objects in the early Universe, and determining their properties, scientists are able to determine how the structures that we are familiar with today – i.e. stars, galaxies, clusters, etc. – truly came from.
These same studies also allow scientists to make educated guesses about where the Universe is going and what will become of those same structures millions or even billions of years from now. In short, knowing where we’ve been lets us predict where we are headed!
Further Reading: arXiv
The most powerful space telescope ever built will have to wait on the ground for a few more months into 2019 before launching to the High Frontier and looking back nearly to the beginning of time and unraveling untold astronomical secrets on how the early Universe evolved – Engineers need a bit more time to complete the Webb telescopes incredibly complex assembly and testing here on Earth.
Blastoff of NASA’s mammoth James Webb Space Telescope (JWST) has been postponed from late 2018 to the spring of 2019.
“NASA’s James Webb Space Telescope now is planning to launch between March and June 2019 from French Guiana, following a schedule assessment of the remaining integration and test activities,” the agency announced.
Until now the Webb telescope was scheduled to launch on a European Space Agency (ESA) Ariane V booster from the Guiana Space Center in Kourou, French Guiana in October 2018.
“The change in launch timing is not indicative of hardware or technical performance concerns,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate at Headquarters in Washington, in a statement.
“Rather, the integration of the various spacecraft elements is taking longer than expected.”
NASA’s says the currently approved budget will not bust the budget or reduce the science output. It “accommodates the change in launch date, and the change will not affect planned science observations.”
NASA’s $8.8 Billion James Webb Space Telescope is the most powerful space telescope ever built and is the scientific successor to the phenomenally successful Hubble Space Telescope (HST).
The Webb Telescope is a joint international collaborative project between NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA).
Since Webb is not designed to be serviced by astronauts, the extremely thorny telescope deployment process is designed to occur on its own over a period of several months and must be fully successful. Webb will be positioned at the L2 Lagrange point- a gravitationally stable spot approximately 930,000 miles (1.5 million km) away from Earth.
So its better to be safe than sorry and take the extra time needed to insure success of the hugely expensive project.
Various completed components of the Webb telescope are undergoing final testing around the country to confirm their suitability for launch.
Critical cryogenic cooling testing of Webb’s mirrors and science instrument bus is proceeding well inside a giant chamber at NASA’s Johnson Space Center in Texas.
However integration and testing of the complex multilayered sunshield at Northrup Grumman’s Redondo Beach, Ca. facility is taking longer than expected and “has experienced delays.”
The tennis court sized sunshield will protect the delicate optics and state of the art infrared science instruments on NASA’s Webb Telescope.
Webb’s four research instruments cannot function without the essential cooling provided by the sunshield deployment to maintain them at an operating temperature of minus 388 degrees F (minus 233 degrees C).
The Webb telescopes groundbreaking sunshield subsystem consists of five layers of kapton that will keep the optics and instruments incredibly cool, by reducing the incoming sunside facing temperature more than 570 degrees Fahrenheit. Each layer is as thin as a human hair.
“Webb’s spacecraft and sunshield are larger and more complex than most spacecraft. The combination of some integration activities taking longer than initially planned, such as the installation of more than 100 sunshield membrane release devices, factoring in lessons learned from earlier testing, like longer time spans for vibration testing, has meant the integration and testing process is just taking longer,” said Eric Smith, program director for the James Webb Space Telescope at NASA Headquarters in Washington, in a statement.
“Considering the investment NASA has made, and the good performance to date, we want to proceed very systematically through these tests to be ready for a Spring 2019 launch.”
Northrop Grumman designed the Webb telescope’s optics and spacecraft bus for NASA’s Goddard Space Flight Center in Greenbelt, Maryland, which manages Webb.
Watch for Ken’s onsite space mission reports direct from the Kennedy Space Center and Cape Canaveral Air Force Station, Florida.
Stay tuned here for Ken’s continuing Earth and Planetary science and human spaceflight news.
Learn more about the upcoming ULA Atlas NRO NROL-52 spysat launch on Oct 5 and SpaceX Falcon 9 SES-11 launch on Oct 7, JWST, OSIRIS-REx, NASA missions and more at Ken’s upcoming outreach events at Kennedy Space Center Quality Inn, Titusville, FL:
Oct 3-6, 8: “ULA Atlas NRO NROL-52 spysat launch, SpaceX SES-11, CRS-12 resupply launches to the ISS, Intelsat35e, BulgariaSat 1 and NRO Spysat, SLS, Orion, Commercial crew capsules from Boeing and SpaceX , Heroes and Legends at KSCVC, ULA Atlas/John Glenn Cygnus launch to ISS, SBIRS GEO 3 launch, GOES-R weather satellite launch, OSIRIS-Rex, Juno at Jupiter, InSight Mars lander, SpaceX and Orbital ATK cargo missions to the ISS, ULA Delta 4 Heavy spy satellite, Curiosity and Opportunity explore Mars, Pluto and more,” Kennedy Space Center Quality Inn, Titusville, FL, evenings