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The Evolutionary Perspective
Category Archives: Astronomy
Astronomy: There are lessons to be learned from transit of Mercury across sun – The Columbus Dispatch
Posted: at 6:42 pm
Observing the transit of an inner planet requires a telescope with a solar filter that allows viewing the sun without eye damage. The transit appears as a small black dot that slowly moves across the face of the sun. It isnt visible without magnifying the suns image.
The transit of Mercury is a bit like what happens in a solar eclipse. Instead of the moon coming between Earth and the sun, which can entirely block the suns light, Mercury is much farther away, so it blocks only a small fraction (less than half a percent) of the sun. But even though its only a small black dot, its clearly visible with the right telescope.
The historical importance of the transit of Mercury goes back to the 1600s, when Johannes Kepler, famous for his planetary orbital laws, was the first astronomer to predict it. Back then, there was still public controversy about the model of Copernicus, where planets go around the sun, and the older view that the sun orbited Earth. The transit of Mercury was first observed in 1631 by French astronomer Pierre Gassendi, and was irrefutable evidence that Copernicus was right.
In 1677, Edmund Halley, for whom Halleys comet is named, realized that he could use the transit of Mercury to find the distance to the sun. He did that by measuring the time of the start and finish of Mercurys shadow as it went across the sun, and then used the mathematical technique of parallax to calculate the distance. This was a tour-de-force calculation for its time.
Today, the transit of Mercury is more of a curiosity than a groundbreaking scientific event. However, an interesting application of this technique has been applied to look for planets around other stars. The NASA space telescope Kepler made very careful measurements of the brightness of stars, and found periodic times when the brightness dipped by about 1%. Thats expected to happen when an exoplanet orbits the star and comes between that star and the view from Earth. Thousands of exoplanets have been discovered using the method.
The transit of planets can be used as a great teaching moment for amateur astronomers, either young or old. Its one thing to learn about the planetary orbits in a textbook, but another entirely to see a planets shadow move across the sun in real time.
Kenneth Hicks is a professor of physics and astronomy at Ohio University in Athens.
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The Institute for Astronomy helped people gathered at Waialae Beach Park to observe the event. PC: University of Hawaii
The planet Mercury did its best Icarus impression last week, and students from the University of Hawai traveled to the Big Island for a chance to witness it.
University of Hawaii astronomers joined many observers around the world in tracking the transit of Mercury on Monday, Nov. 11. A transit is when a planet passes in front of a star. Mercury and Venus are the only two planets that can be observed from Earth in transit.
About 30 UH Mnoa students flew to Hawaii Island to view the event at the Subaru Telescope as part of a group of around 200 people to use solar telescopes.
UH Mnoas Institute for Astronomy held a viewing party at Waialae Beach Park for more than 100 people.
Mercury takes just 88 days to circle the Sun. It passes between the Sun and Earth frequently but usually out of view.
The transit of Mercury will not be seen from Earth again until November 2032, and not from Hawaii until 2049. The next transit of Venus will not be visible from Earth until 2117.
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Innermost planet Mercury puts on its best morning display of the year for Northern Hemisphere observers from late November to early December. Skywatchers in the British Isles should find a location offering an unobstructed view of the southeast horizon about 45minutes before sunrise to get the best views. This looping animation shows the changing configuration of Mercury, Mars and Virgos brightest star, Spica, from 18November through 3December at dawn. Note the span of a fist at arms length (about 10) for scale, but the Moons apparent size on 24 and 25November has been enlarged for clarity. AN animation by Ade Ashford.Mercurys transit of the Sun on 11November is still fresh in the memory, but it doesnt take long for the innermost planets orbital motion to carry it far enough west of the Sun to be visible low above the southeastern horizon in dawn twilight. Mercury attains its greatest westerly elongation of 20degrees on the UK morning of 28November. In fact, for Northern Hemisphere observers, the remainder of the month into early December offers Mercurys best morning viewing prospects for the entire year.
Any opportunity to get a glimpse of this elusive and fast-moving planet is well worth getting up a little earlier for, particularly when as now you get a chance to see Mars nearby at the same time. As with any observation made in the eastern sky during dawn twilight, timing is everything: you need to view late enough that Mercury gets a chance to rise high enough above the horizon murk, but not so late that impending sunrise makes the sky too bright to see it. (Never look anywhere near the Sun after it has risen.)
Observers in the British Isles need to find a location that offers an unobscured view of the southeast horizon about three-quarters of an hour before sunrise between now and the first week of December. Our interactive online Almanac gives you the time of sunrise for your nearest town or city, so just subtract 45minutes from that.The slim crescent of the 27-day-old waning Moon lies slightly less than 4degrees above magnitude +1.7 Mars at UK dawn on Sunday, 24November 2019, hence the pair will fit in the same field of view of 10 and lower magnification binoculars. On this morning, the Red Planet sits midway between magnitude -0.2 Mercury and first-magnitude star Spica in Virgo. Note that the Moons apparent size has been enlarged for clarity in this illustration. AN graphic by Ade Ashford.Mercury is located in the constellation of Libra for the period illustrated in the animation at the top of the page. The planet lies about 9degrees (almost the span of a fist held at arms length) above the southeast horizon at the optimal viewing time between 23November and the beginning of December. The Red Planet sits midway between Mercury and the first-magnitude star Spica, the brightest in the constellation of Virgo, at UK dawn on 24November.
Magnitude +1.7 Mars remains in Virgo until the morning of 1December when it crosses the constellation border to join Mercury in Libra. Mercury brightens more than fourfold from magnitude +1 to -0.6 during the 18November to 3December observing window. If clear, dont miss the binocular highlights of 24 and 25November at dawn when the old waning crescent Moon lies 4 above Mars and 3 to the lower left of Mercury, respectively.
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China made history earlier this year when its Chang'e-4 lander became the first spacecraft to land on the far side of the moon. During the two-week lunar days, the lander and its small rover, Yutu 2, beam images and other data to an orbiter for relay back to Earth. Together theyve furnished planetary scientists with unprecedented access to the backside of our Janus-faced neighbor. But not everyone was thrilled that China crossed into this new lunar frontier, and few have been more vocal about their concerns than the scientists involved in the search for extraterrestrial intelligence.
Last month, the SETI permanent committee of the International Astronautical Association hosted its second round of negotiations about the lunar farside in Washington, DC. The exploration of the moon might seem like an issue outside the purview of this group of professional alien hunters, but the far side of the moon is the most radio quiet place in the inner solar system and they want to keep it that way in case ET calls. Indeed, they argue that the fate of the lunar farside may determine whether we ever detect a signal from an extraterrestrial intelligence.
At the moment, SETI is not doomed, but it might be doomed in the next 50 years and thats being optimistic, says Claudio Maccone, an astrophysicist and the chair of the IAA SETI committee. We must insist on this topic while there is still time to do something.
On Earth, radio astronomers must contend with interference from television broadcasts, cell phone signals, satellites, and the atmosphere as they scan the cosmos for faint signals from primordial stars, organic molecules, or intelligent life. This makes the lunar farside an attractive site for future radio telescopes because the moon blocks all the radio signals from Earth. Its like the difference between stargazing in New York City and stargazing in the middle of the desertin the city light pollution obscures almost all of the good stuff.
As a hedge against the unchecked proliferation of radio frequency interference, a radio astronomer named Jean Heidmann made the case for a SETI radio base on the far side of the moon back in the mid-90s. Even before cell phones became common, Heidmann realized that radio interference could eventually become so bad that searching for aliens with radio telescopes would be impossible on Earth. Moving radio observatories to the moon wouldnt require turning the entire lunar farside into a radio quiet zone, but it would guarantee that at least some portions of the moon are preserved for radio astronomy and the hunt for extraterrestrial intelligence.
Here on Earth, governments could create more radio quiet zones like the kind around the National Radio Astronomy Observatory in Green Bank, West Virginia, but even then we might miss a message from ET. The Earths atmosphere starts to block out radio frequencies as you move away from a relatively narrow frequency band called the microwave window, so unless ET happens to be transmitting on one of those frequencies wed struggle to hear it. But the lunar atmosphere is virtually nonexistent, which means radio astronomers would have access to frequencies above and below Earths microwave window. And, given the moons low gravity environment, astronomers would also be able to build massive radio telescopes that dwarf those found on Earth.
After Heidmanns death in 2000, Maccone took up the cause of preserving the lunar farside for radio astronomy. He has written several papers on the subject and even gave a presentation to the United Nations, but until recently his pleas have fallen on deaf ears. The reason, Maccone says, is that the issue lacked any urgency. Most national space agencies had neither the funding nor the will to launch a mission to the far side of the moon and billionaires were still struggling just to get a rocket to orbit.
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Solidity is a function of magnification. We know that anything we experience as solid is actually a structure of atoms packed closely enough that to our eyes they appear to be a single solid thing. If we were small enough, we'd see the spaces between them; if we were even smaller, those spaces might seem vast. Likewise, in 1989 Margaret Geller and John Huchra, analyzing redraft survey data, discovered the immense "Great Wall," a "sheet" formed from galaxies many light years apart. That first large-scale structure is 500 million light-years long, 200 million light years wide, and with a thickness of 15 million light years.
Other gigantic large-scale structures been discovered since sheets, filaments, and knots, with bubble-like voids intersperse among them. They appear to be connected by clouds and filaments of hydrogen gas and dark matter. Though the bodies that comprise the structures are not gravitationally bound to each other the distances between them are too great evidence is piling up that they are linked by something.
Recent observations indicate that galaxies far, far apart are somehow synchronously moving. Something appears to be binding large-scale structures, many light years apart, together after all. Is the currently accepted view of the universe as various clumps of material simply expanding outward from the Big Bang and gravitationally pulling on each other wrong?
The existence and mechanics of large-scale structures are a tantalizing puzzle with obviously major implications for our understanding of the universe. As Noam Libeskind, of the Leibniz-Institut for Astrophysics (AIP) in Germany tells VICE, "That's actually the reason why everybody is always studying these large-scale structures. It's a way of probing and constraining the laws of gravity and the nature of matter, dark matter, dark energy, and the universe."
The identification and study of large-scale structures is a product of analyzing and modeling simulations of redshift survey for specific regions of the sky that visually reveal these immense structures.
The large-scale structures revealed in one segment of sky
Image source: National Center for Supercomputer Applications by Andrey Kravtsov (The University of Chicago) and Anatoly Klypin (New Mexico State University). Visualizations by Andrey Kravtsov.
Several pieces of research are causing interest in these large-scale structures to heat up. The most mind-blowingly distant synchronized motion was reported in 2014, when the rotation axes of 19 super-massive black holes at the centers of quasars out of 100 quasars studied were found to be in alignment, billions of light years apart. According to the study's lead author, astronomer Damien Hutsemkers of the University of Lige in Belgium, "Galaxy spin axes are known to align with large-scale structures such as cosmic filaments but this occurs on smaller scales. However, there is currently no explanation why the axes of quasars are aligned with the axis of the large group in which they are embedded."
The first word of the research paper's title, "Spooky Alignment of Quasars Across Billions of Light-years," invokes cosmic-scale quantum entanglement as a possible explanation.
Image source: orin/Shutterstock/Big Think
Astronomer Joon Hyeop Lee of the Korea Astronomy and Space Institute is the lead author of "Mysterious Coherence in Several-megaparsec Scales between Galaxy Rotation and Neighbor Motion," published in October of this year in Astrophysical Journal. Comparing data from two catalogs of redshift survey data the Calar Alto Legacy Integral Field Area (CALIFA) and NASA-Sloan Atlas (NSA) catalogs the researchers' analysis of 445 galaxies revealed, surprisingly, that galaxies six meparsecs, or 20 million light years, apart were moving in the same way. Those observed, for example, a galaxy moving toward the Earth was mirrored by other distant galaxies moving in the same direction.
"This discovery is quite new and unexpected," according to Lee, "I have never seen any previous report of observations or any prediction from numerical simulations, exactly related to this phenomenon."
Since the galaxies are too distant for their gravitational fields to be influencing each other, Lee poses another explanation: That the linked galaxies are both embedded within the same, large-scale structure.
Image source: sripfoto/Shutterstock/Big Think
Another puzzle suggesting the influence of large-scale structures has become clear over recent years. It's been observed that galaxies surrounding our own Milky Way are weirdly arranged in a single, flat plane. Big-Bang thinking would suggest that they should be circling us at all different sorts of angles. Obviously, for adherents of that way of viewing the galaxy known as the CDM model this at the very least a troubling anomaly.
The hope that it was an anomaly weakened with the discovery of the same thing occurring around the Andromeda galaxy, and then again around Centaurus A in 2015. By the time "A whirling plane of satellite galaxies around Centaurus A challenges cold dark matter cosmology" was published in 2018, the phenomenon was starting to seem quite common, and possibly universal. The idea that the satellite galaxies might part of a large-scale structure had become even worthier of serious consideration.
As more astronomers embrace the notion of large-scale structures and related research accelerates, we can only hope that these perplexingly oddball movements and associations are eventually made clear. Certainly, imagining a vast arrangement of utterly gigantic structures in which galaxies are embedded paints a very different picture of the universe, and one that makes one wonder if these structures are themselves embedded in something even larger. In this mid-boggling case, we are indeed small enough to see only the space between objects in this case galaxies. We've been no more aware of them than whatever it is that may be living between our own atoms.
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Astronomers have confirmed the first example of a galaxy cluster where large numbers of stars are being born at its core. Using data from NASA space telescopes and a National Science Foundation radio observatory, researchers have gathered new details about how the most massive black holes in the universe affect their host galaxies.
Galaxy clusters are the largest structures in the cosmos that are held together by gravity, consisting of hundreds or thousands of galaxies embedded in hot gas, as well as invisibledark matter. The largest supermassive black holes known are in galaxies at the centers of these clusters.
For decades, astronomers have looked for galaxy clusters containing rich nurseries of stars in their central galaxies. Instead, they found powerful, giant black holes pumping out energy through jets of high-energy particles and keeping the gas too warm to form many stars.
Now, scientists have compelling evidence for a galaxy cluster where stars are forming at a furious rate, apparently linked to a less effective black hole in its center. In this unique cluster, the jets from the central black hole instead appear to be aiding in the formation of stars. Researchers used new data from NASAs Chandra X-ray Observatory and Hubble Space Telescope, and the NSFs Karl Jansky Very Large Array (VLA) to build on previous observations of this cluster.
This is a phenomenon that astronomers had been trying to find for a long time, said Michael McDonald, astronomer at the Massachusetts Institute of Technology (MIT), who led the study. This cluster demonstrates that, in some instances, the energetic output from a black hole can actually enhance cooling, leading to dramatic consequences.
The black hole is in the center of a galaxy cluster called the Phoenix Cluster, located about 5.8 billion light years from Earth in the Phoenix Constellation. The large galaxy hosting the black hole is surrounded by hot gas with temperatures of millions of degrees. The mass of this gas, equivalent to trillions of Suns, is several times greater than the combined mass of all the galaxies in the cluster.
This hot gas loses energy as it glows in X-rays, which should cause it to cool until it can form large numbers of stars. However, in all other observed galaxy clusters, bursts of energy driven by such a black hole keep most of the hot gas from cooling, preventing widespread star birth.
Imagine running an air conditioner in your house on a hot day, but then starting a wood fire. Your living room cant properly cool down until you put out the fire, said co-author Brian McNamara of the University of Waterloo in Canada. Similarly, when a black holes heating ability is turned off in a galaxy cluster, the gas can then cool.
Evidence for rapid star formation in the Phoenix Cluster was previously reported in 2012 by a team led by McDonald. But deeper observations were required to learn details about the central black holes role in the rebirth of stars in the central galaxy, and how that might change in the future.
By combining long observations in X-ray, optical, and radio light, the researchers gained a ten-fold improvement in the data quality compared to previous observations. The new Chandra data reveal that hot gas is cooling nearly at the rate expected in the absence of energy injected by a black hole. The new Hubble data show that about 10 billion solar masses of cool gas are located along filaments leading towards the black hole, and young stars are forming from this cool gas at a rate of about 500 solar masses per year. By comparison, stars are forming in the Milky Way galaxy at a rate of about one solar mass per year.
The VLA radio data reveal jets blasting out from the vicinity of the central black hole. These jets likely inflated bubbles in the hot gas that are detected in the Chandra data. Both the jets and bubbles are evidence of past rapid growth of the black hole. Early in this growth, the black hole may have been undersized, compared to the mass of its host galaxy, which would allow rapid cooling to go unchecked.
In the past, outbursts from the undersized black hole may have simply been too weak to heat its surroundings, allowing hot gas to start cooling, said co-author Matthew Bayliss, who was a researcher at MIT during this study, but has recently joined the faculty at the University of Cincinnati. But as the black hole has grown more massive and more powerful, its influence has been increasing.
The cooling can continue when the gas is carried away from the center of the cluster by the black holes outbursts. At a greater distance from the heating influence of the black hole, the gas cools faster than it can fall back towards the center of the cluster. This scenario explains the observation that cool gas is located around the borders of the cavities, based on a comparison of the Chandra and Hubble data.
Eventually the outburst will generate enough turbulence, sound waves and shock waves (similar to the sonic booms produced by supersonic aircraft) to provide sources of heat and prevent further cooling. This will continue until the outburst ceases and the build-up of cool gas can recommence. The whole cycle may then repeat.
These results show that the black hole has temporarily been assisting in the formation of stars, but when it strengthens its effects will start to mimic those of black holes in other clusters, stifling more star birth, said co-author Mark Voit of Michigan State University in East Lansing, Michigan.
The lack of similar objects shows that clusters and their enormous black holes pass through the rapid star formation phase relatively quickly.
A paper describing these results was published in a recent issue of The Astrophysical Journal, and a preprint isavailable online.
NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science and flight operations from Cambridge and Burlington, Massachusetts. The NASA Hubble Space Telescope is a project of international cooperation between NASA and ESA. AURAs Space Telescope Science Institute in Baltimore, Maryland conducts Hubble science operations. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
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A new study, published in the journal Icarus, shows that Naiad and Thalassa, two innermost moons of Neptune, are locked in an unusual type of orbital resonance.
The odd orbits of Neptunes inner moons Naiad and Thalassa enable them to avoid each other as they race around the giant planet. Image credit: Brozovi et al, doi: 10.1016/j.icarus.2019.113462.
Far from the pull of the Sun, giant planets are the dominant sources of gravity, and collectively, they boast dozens upon dozens of moons.
Some of those moons formed alongside their planets and never went anywhere; others were captured later, then locked into orbits dictated by their planets. Some orbit in the opposite direction their planets rotate; others swap orbits with each other as if to avoid collision.
The Neptune system consists of seven regular inner moons, Triton, Nereid, and five irregular outer moons.
Inner moons Naiad and Thalassa were discovered by NASAs Voyager 2 spacecraft during the 1989 flyby of Neptune.
They are about 60 miles (100 km) in length and are true partners, orbiting only about 1,150 miles (1,850 km) apart.
But they never get that close to each other; Naiads orbit is tilted and perfectly timed. Every time it passes the slower-moving Thalassa, the two are about 2,200 miles (3,540 km) apart.
In this perpetual choreography, Naiad swirls around Neptune every seven hours, while Thalassa, on the outside track, takes seven and a half hours.
An observer sitting on Thalassa would see Naiad in an orbit that varies wildly in a zigzag pattern, passing by twice from above and then twice from below.
This up, up, down, down pattern repeats every time Naiad gains four laps on Thalassa. Although the dance may appear odd, it keeps the orbits stable.
Dr. Marina Brozovi, a researcher at NASAs Jet Propulsion Laboratory, and colleagues discovered the unusual orbital pattern using analysis of observations by the NASA/ESA Hubble Space Telescope.
We refer to this repeating pattern as a resonance. There are many different types of dances that planets, moons and asteroids can follow, but this one has never been seen before, Dr. Brozovi said.
So how did Naiad and Thalassa end up together but apart? Its thought that the original satellite system was disrupted when Neptune captured its giant moon, Triton, and that these inner moons and rings formed from the leftover debris.
We suspect that Naiad was kicked into its tilted orbit by an earlier interaction with one of Neptunes other inner moons, Dr. Brozovi said.
Only later, after its orbital tilt was established, could Naiad settle into this unusual resonance with Thalassa.
The study also provides the first hint about the internal composition of Neptunes inner moons.
The scientists used the Hubble observations to compute their mass and, thus, their densities which were close to that of water ice.
We are always excited to find these co-dependencies between moons, said Dr. Mark Showalter, a planetary astronomer at the SETI Institute.
Naiad and Thalassa have probably been locked together in this configuration for a very long time, because it makes their orbits more stable. They maintain the peace by never getting too close.
Marina Brozovi et al. 2020. Orbits and resonances of the regular moons of Neptune. Icarus 338: 113462; doi: 10.1016/j.icarus.2019.113462
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"I Love the Sense of Discovery." Dr. Eric Wilcots Stays Focused on Science as he Ascends Academic Ladder – madison365.com
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For the past quarter-century, Eric Wilcots has been one of the University of WisconsinMadisons most prominent astronomers.
I love the sense of discovery, he says. We get to discover things. As a scientist I was fascinated by how the universe works: to be able to see things and understand things that other people have not seen, to be able to see them in a different way, to be able to ask really big blue-sky science questions like, How do galaxies change over time? Thats just compelling and fascinating to understand how the universe works and how this planet that we live on got to be here. Its fascinating.
Although astronomy has been his lifes passion, Wilcots is currently providing the leadership for the College of Letters & Science, the largest college at the UW. He has served as the Mary C. Jacoby professor of astronomy, deputy dean, and associate dean for research. On August 5, he became the colleges interim dean when predecessor John Karl Scholz was appointed as the universitys next provost.
We do lots of really good things here, so its an exciting opportunity for me, Wilcots says.
Wilcots has been an important role model and mentor for younger people of color interested in the STEM (science, technology, engineering, and math) fields, which have historically lacked the diversity of the general population.
I think that its so important, Wilcots says. We live in a world in this day and age where we can think of science as driving a lot of what we do. A lot of problems that we wrestle with need to be addressed via science. Yet the scientific community writ large is not tapping the talent that it can. So diversifying the STEM discipline is more than just embracing diversity. Its recognizing that we are shorting ourselves if we are not tapping all of the talent across all populations. To the extent that I can be a role model and to the extent that theres a kid out there who sees someone doing science that kind of looks like me thats wonderful. Im humbled by that.
Wilcots first became fascinated by astronomy as a little boy in Philadelphia.
I got a telescope for Christmas when I was eight or nine, and thats what piqued my interest in astronomy, Wilcots says. I remember watching theVoyager 1[probe] flying by Jupiter for about a week, and there were all these fantastic images coming back from Jupiter. The people looked like they were having fun. I remember thinking, I want to do that! Whatever that was, I wanted to be a part of it.
Wilcots spent a couple of years working at the Franklin Institute Science Museum in Philadelphia, one of Americas most celebrated museums.
The observatory was my favorite place to be in that building, Wilcots remembers.
Wilcots went on to earn his bachelors degree in astrophysics at Princeton University in 1987 and a PhD in astronomy from the University of Washington in 1992. From 1992 to 1995, he was a Karl Jansky Postdoctoral Fellow at the National Radio Astronomy Observatory in Socorro, New Mexico, before coming to UWMadison.
I came here in 95. The intellectual curiosity that I see is invigorating. I love that kind of environment, Wilcots says. We have fantastic students who come through who are remarkable and inspiring in their own way. We have students who could have gone [to college] anywhere, and they decided to come here. Wisconsin is a great place to be.
Wilcotss research interests focus on understanding the evolution of galaxies and galaxy groups, primarily through observations of radio wavelengths, and he loves sharing the process of discovery with UW students.
Ive had a fantastic set of graduate students over the years and an equally fantastic group of undergraduates that Ive worked with. To be able to have a student come in who is unfamiliar with the discipline but then come out of that process with that sense of discovery themselves, thats pretty cool, he says. Working with students is a fun part of the job. I would not want to be an astronomer and not want to work with students.
Posted: November 17, 2019 at 1:43 pm
The remnant of supernova 1987a, located in the Large Magellanic Cloud some 165,000 light years away.... [+] When they reach peak brightness, a type II (core-collapse) supernova will be more than twice as bright as a type Ia supernova ever will be, and will emit both neutrinos and light simultaneously, but that interact differently with their environment and hence arrive at different times.
On February 24, 1987, a spectacular signal was seen as never before. From 165,000 light-years away, the first signals from a recently destroyed star a core-collapse supernova arrived on Earth. Humans had witnessed supernovae before, both within the Milky Way and in galaxies beyond our own, but this one was special. The first hint of its arrival didn't come in the form of light, but rather in a signal never measured before: in the form of neutrinos.
It wasn't until hours later that the light arrived, corresponding to the extra time it took the shock wave occurring in the star's interior to reach the surface. Whereas light interacts with the material composing the progenitor star, neutrinos simply pass right through it, giving them a significant head start. For the first time, an astronomical event beyond our Solar System had emitted both light and particles that were observed on Earth. The era of Multi-Messenger Astronomy was born. Although it's still a term that few non-astronomers are familiar with, it truly is the future of studying the Universe.
Multiple neutrino events, reconstructed from separate neutrino detectors. In 1987, three independent... [+] detectors that were sensitive to energetic neutrinos and antineutrinos detected a total of 25 particles in a single burst spanning 13 seconds. A few hours later, the light arrived as well.
Originally, astronomy was confined to a very narrow regime: the only signals we were capable of receiving were in the form of visible light. Since that's what our eyes had adapted to see, those were the tools we had at our disposal to examine the Universe. For countless millennia, human eyes viewed the Sun, Moon, planets, stars, and the fuzzy, distant nebulae we now know to be galaxies as they slowly but surely migrated across the sky.
Even after the invention of the telescope, astronomy was still confined to what we could perceive in visible light. All the telescope did, essentially, was to enhance our light-gathering power by using mirrors and/or lenses to increase the light-collecting area far beyond the limits of even the most thoroughly dilated pupil. Instead of thousands of stars, these tools would reveal hundreds of thousands, millions, and eventually billions of them.
A map of star density in the Milky Way and surrounding sky, clearly showing the Milky Way, the Large... [+] and Small Magellanic Clouds (our two largest satellite galaxies), and if you look more closely, NGC 104 to the left of the SMC, NGC 6205 slightly above and to the left of the galactic core, and NGC 7078 slightly below. In visible light, only starlight and the presence of light-blocking dust is revealed, but other wavelengths have the capacity to reveal fascinating and informative structures far beyond what the optical part of the spectrum can.
Early on, only the brightest objects appeared to have color features; the others were so far away that only monochrome signals were perceptible.When photographic techniques became available and were applied to astronomy, however, it became possible toplace a color filter over the telescope, recording only light of a particular wavelength.
When multiple different wavelengths were sampled either at once or in rapid succession, the data that was collected could be combined to form a single color image. This technique was originally applied to terrestrial images, but was extended to astronomy in short order, enabling scientists to produce color images of objects in the night sky. Even today, the field of astrophotography is enjoyed by not only professionals, but tens of thousands of amateurs and hobbyists from across the world.
By taking three different photographs of the same object that collect data at three different... [+] wavelengths, colors (like red, green, and blue) can be assigned and added together, producing an image that looks true-to-life and in real color to our eyes. Astronomers not only use this technique, but have extended it to beyond the limits of our eyes by implementing multi-wavelength astronomy.
Still, this advance only leveraged the tiniest portion of the electromagnetic spectrum: visible light. In reality, there are many forms of light that are both higher in energy (and shorter in wavelength) as well as lower in energy (with longer wavelengths) that can be perceived and measured by the right type of telescope.
Today, we take advantage of all the different forms of light that there are to study the objects present in the Universe.
Whenever we look at an object in a different wavelength of light, we have the potential to reveal an entirely new class of information about it.
This multi-wavelength view of the nearby Andromeda galaxy shows what is revealed in radio, infrared,... [+] visible, ultraviolet, and X-ray light. Gas, dust, stars, and stellar remnants that emit light in different energies and at different temperatures can all be highlighted, dependent on which wavelength is chosen.
Even though we have different names for these various types of astronomical observing some of what we observe are rays (gamma-rays and X-rays), some are light (ultraviolet and visible), some are radiation (infrared) and some are waves (radio) they're all still light. From a physics point of view, we're collecting the same thing: photons, or quanta of light. We're just looking at light with different properties when we're doing any of these types of astronomy.
In other words, doing astronomy by collecting light of any type always involves the same type of messenger: the same type of information-carrier. However, there are other forms of astronomy, too, because the objects in the Universe doesn't just emit light. As they undergo all the various astrophysical processes that the Universe allows, they can emit a wide variety of classes of signal, including from fundamentally different messengers.
Cosmic rays, which are ultra-high energy particles originating from all over the Universe, strike... [+] protons in the upper atmosphere and produce showers of new particles. The fast-moving charged particles also emit light due to Cherenkov radiation as they move faster than the speed of light in Earth's atmosphere, and produce secondary particles that can be detected here on Earth.
Numerous classes of objects don't merely emit light, but also particles. From all over the sky, including from the Sun, we detect a wide variety of cosmic ray particles, including:
We've been collecting these types of particles from within the Solar System for extremely long periods of time, as arguably every time we encounter a meteor shower, we're witnessing particle showers in our atmosphere originating from past-and-present comets. The Sun emits a wide variety of cosmic rays. And recently, with sophisticated observatories like Kamiokande (and its successors) and IceCube, we're detecting both solar and cosmic neutrinos.
The Super-Kamiokande detector, the successor to the neutrino observatory responsive for 12 of the 25... [+] neutrinos seen in the nearby 1987 supernova, was able to produce this image of the Sun from the solar neutrinos alone.
Light and particles are each a completely independent type of "messenger" in astronomy, as they require fundamentally different techniques, equipment, and interpretations in order to make sense of the Universe. But the 2010s brought us something even more remarkable: a third type of fundamental messenger. On September 14, 2015, the first new signal arrived: in the form of gravitational waves.
Gravitational waves are the only signal ever directly detected that has no type of known, measured, Standard Model particle associated with it. They are generated whenever a massaccelerates through a region of space that changes in its curvature, but it's only the strongest, largest-amplitude signals of a specific frequency that we're able to detect. Using a large, extraordinarily precise laser interferometer, scientists are able to detect gravitational waves that correspond to a change in those arm lengths of no more than 10-19 meters: about 1/10,000th the width of a proton.
The LIGO Hanford Observatory for detecting gravitational waves in Washington State, USA, relies on... [+] two perpendicular, 4 km arms with lasers inside them to detect the passage of gravitational waves. When a wave passes through, one arm will contract while the other expands and vice versa, creating an oscillatory signal with an amplitude of just ~10^-19 meters.
With three fundamentally different types of astronomy, we've gained new windows on the Universe and new methods of gaining information about all that's out there. Light, particles, and gravitational waves are intrinstically different types of messengers for astronomers, with each class of signal revealing information about the Universe that the other two cannot.
But the most powerful examples of these various astronomical techniques occur when we're able to use more than one of them at the same time. When astronomers use the term "Multi-Messenger Astronomy," this is the key concept they're referring to: detecting the same object or event with either light and particles, light and gravitational waves, particles and gravitational waves, or all three together. As the sciences of traditional (light-based) astronomy, gravitational wave astronomy, and cosmic ray astronomy all advance, these multi-messenger events will reveal the Universe as never before.
Artists illustration of two merging neutron stars. The rippling spacetime grid represents... [+] gravitational waves emitted from the collision, while the narrow beams are the jets of gamma rays that shoot out just seconds after the gravitational waves (detected as a gamma-ray burst by astronomers). The aftermath of the neutron star merger observed in 2017 points towards the creation of a black hole.
In 2017, gravitational wave astronomers observed a signal unlike any other, which wound up corresponding to the merger of two neutron stars some 130 million light-years away. Almost simultaneously just two seconds after the gravitational wave signal ceased the first electromagnetic signal (in the form of gamma-rays) arrived. The first robust multi-messenger signal involving gravitational waves had been detected.
This is only going to get better with time and improved technology. When the next nearby supernova occurs, we'll certainly be able to detect both light and particles, and might even get gravitational waves, too. In fact, we had a candidate (that didn't pan out) for our first trifecta signal earlier this year. When a pulsar glitch is picked up by a gravitational wave detector, it will also be a multi-messenger signal. And when LISA, our next-generation gravitational wave detector comes online, we'll even be able to predict these cosmic mergers that LIGO and Virgo see today well in advance, giving ourselves plenty of lead time to make simultaneous observations of a possible multi-messenger event at that critical, "t=0" moment.
The primary scientific goal of the Laser Interferometer Space Antenna (LISA) mission is to detect... [+] and observe gravitational waves from massive black holes and galactic binaries with periods in the range of a tens of seconds to a few hours. This low-frequency range is inaccessible to ground-based interferometers because of the unshieldable background of local gravitational noise arising from atmospheric effects and seismic activity. Its arrival could herald a new, monumental advance in multi-messenger astronomy.
The three types of signals we know how to collect from the Universe light, particles, and gravitational waves all deliver fundamentally different types of information right to our front door. By combining the most precise observations we can take with each of these, we can learn more about our cosmic history than any one of these signal types, or "messengers," can provide in isolation.
We've already learned how neutrinos are produced in supernova, and how their travel path is less impeded by matter than light's is. We've already linked merging neutron stars with kilonovae and the production of the heaviest elements in the Universe. With multi-messenger astronomy still in its infancy, we can expect a deluge of new events and new discoveries as this science progresses throughout the 21st century.
Just as you can learn more about a tiger by hearing its growl, smelling its scent, and watching it hunt than you can from a still image alone, you can learn more about the Universe by detecting these fundamentally different types of messengers all at once. Our bodies might be limited in terms of the senses we can use in any given scenario, but our knowledge of the Universe is limited only by the fundamental physics governing it. In the quest to learn it all, we owe it to humanity to use every resource we can muster.
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