Artificial gravity is a concept that is ubiquitous in our science fiction yet elusive in our space program. Why is this? And how could we develop artificial gravity soon? In a Cool Worlds special, this video essay goes in depth on the topic discussing why centrifuges are the most plausible solution and early ideas on the topic. Join us a journey from Einstein's equivalence principle, to O'Neill Cylinders and Stanford Tori; from Coriolis forces to near-term experiments. Grab a cup of a tea and enjoy.

Very few people have been lucky enough to see our home planet from Space, but thanks to the incredible spacecraft that are exploring or have already explored neighbouring celestial objects, we get to view amazing footage of the Earth from all over the solar system. So what does Earth look like from deep space?

Can’t get enough of Earth? Then this is for you: an extended playback of Ultra High Definition views of Planet Earth, captured by NASA astronaut Jeff Williams during his mission on the International Space Station in 2016. You’ll see the French Riviera and the Sahara Desert, cross North America from Texas all the way to Canada, and more—this is your source for the view of your home planet from 250 miles up!

These high-res time-lapse sequences captured by astronauts aboard the International Space Station give us a beautiful and clear view of some well-known coastlines and countries around the world. Get a good look at England, France, Italy, Egypt, Algeria, Tunisia, Greece, the island of Crete, Taiwan, South Korea, Japan, the United States, Mexico, Ecuador, Peru, Chile, Argentina, Cuba, and more. We've attempted to show as many countries as we would, but inevitably we've left many out. Please write to the the astronaut photography office at NASA's Johnson Space Center to request inclusion in this amazing series of sequences.

Планетата Земја, видена од вселената - Macedonian Երկիր մոլորակը տիեզերքից - Armenian Planeta Terra visto do espaço - Português (Brasil) Ο Πλανήτης ΓΗ από το Διάστημα - Ελληνικά (Hellenic Language) Il Pianeta Terra visto dallo spazio - Italian Pamântul văzut din spațiu - Romanian / Moldavian language Космостан қарағандағы Жер ғаламшары - kazakh Yerin kosmosdan görünüşü - Azerbaijani Yerin uzaydan görünüşü - Azerbaijani Ang Daigdig mula sa kalawakan - Filipino/Tagalog Jorden fra rommet - Norwegian Jorden set fra rummet - Danish პლანეტა დედამიწის შეხედვა კოსმოსიდან - Georgian Planeta terra visto do espaço - Português Planeta Terra visto do Espaço - Brazilian portuguese ji ezman dîmen ê Erd ê (Kurdish) Planet Erde vom Weltraum aus betrachtet - (German) maa avaruudesta nähtynä - (Finnish) uzaydan dünyanın görünümü (Turkish) Planeti Toke pare nga hapesira - Shqip (Albanian) මිහිතලය අභ්‍යවකාශයේ සිට පෙනෙන ආකාරය. - (Sinhalese, Sri Lanka) эх дэлхий сансараас - (Mongolian) Planeti Toke pare nga hapesira - Shqip (Albanian) ดาวเคราะห์โลกเมื่อมองจากอวกาศ (Thai) 우주에서 본 지구 - (Korean) "Земля з космосу" - (Ukrainian) Planeta Pamant vazuta din spatiu - (Romanian) A Föld az Űrből - (Hungarian) "Ziemia widziana z kosmosu" - (Polish) Земята от космоса - (Bulgarian) "Планета Земля из космоса" - (Russian) "Zeme ir redzama no kosmosa" - (Latvian) meeraha dhulka hawada laga arko - (Somali) An Domhain ó spás - (Irish) "de Aarde gezien vanuit de ruimte" - Dutch رؤية كوكب الأرض من الفضاء. - Arabic "Terra vista do espaço" Terra vista des de l'espai "Earth seen from space" "la terre vue de l'espace" "la tierra desde el espacio" "El planeta Tierra visto desde el espacio" (spanish) "terra vista dallo spazio" โลกดาวเคราะห์เห็นได้จากพื้นที่ يبلغ حجم القمر ربع حجم الأرض ولا يوجد فيه لا هواء ولا ماء ولا حياة. 從太空中看到地球 从太空中看到地球 宇宙から見た地球 Zemlje vidi iz svemira Zemlja iz svemira Země z vesmíru Earth séð frá geimnum પૃથ્વી જગ્યા માંથી જોઇ Jorden set fra rummet Maa kosmosest vaadatuna Maan avaruudesta nähtynä Γη από το διάστημα ഭൂമി ബഹിരാകാശത്തില്‍ നിന്നും כדור הארץ כפי שנראה מהחלל ಭೂಮಿಯ ಜಾಗವನ್ನು ಕಂಡಂತೆ पृथ्वी अंतरिक्ष से देखा Aarde gezien vanuit de ruimte Bumi dilihat dari angkasa Jörð séð frá geimnum Uzaydan Dünyaya Bakış 지구는 우주에서 본 Žemės vaizdas iš kosmoso Zemes redzams no kosmosu Jorden sett fra verdensrommet Pământ văzut din spaţiu Zemlji videl iz vesolja Jorden sedd från rymden Dünya, uzayın görülen Yer kosmik göründüyü Trái đất nhìn từ không gian Terra vista dallo spazio كوكب الارض كما يظهر من الفضاء " زمین از فضا دیده می شود زمین کی خلا سے دیکھا منظر الأرض من الفضاء (Arabic) Gweld Ddaear o'r gofod பூமியை விண்வெளியில் இருந்து பார்க்கும் โลกเห็นได้จากพื้นที่ Kuonekana duniani kutoka nafasi Земље види из свемира Երկրի երեւում է տիեզերքից Dinja tidher mill-ispazju Latè te wè li nan lespas Земјата се гледа од вселената "blue marble"

The International Space Station’s High Definition Earth Viewing (HDEV) experiment is an external camera platform located on the Columbus module of the space station. In addition to providing beautiful views of Earth, one of the goals of HDEV is to monitor the longevity and quality of its image sensors in the space environment. HDEV operations began April 30, 2014 and only a single bad pixel has been identified. Testing new engineering processes and camera system longevity expanded into having avid Earth-viewing followers and educational activities. To date, HDEV has reached over 300 million total views on UStream.

How did the universe come into existence? The singular answer that pops in the heads of pretty much everyone on the face of the earth is “The Big Bang Theory.” It does not take a scientist to be aware of this term, with a lot of the present generation having a very (note the term “very”) brief understanding of the big bang theory thanks to the opening theme of the popular television series of the same name. For those of you who have forgotten (we understand it isn’t the easiest thing to remember), the theory states that the universe started as an infinitely small, dense point called a singularity. All of a sudden, within a trillionth of a second, it expanded rapidly at a rate faster than the speed of light forming what we know as the universe today. The universe is unbelievably vast and carries an enigma of the same magnitude making any theory related to it, only ever partially correct. While the big bang theory is the most widely accepted one of them all, scientists have always known that it certainly isn’t entirely accurate. So what caused the birth of the known universe? A possibility is being considered where a singularity probably never existed in which case the universe grew at a far more comprehensible speed than originally assumed, relatively speaking. Relative to what you ask? It is now believed that expansion had happened before the big bang, thus proving it to not be the starting point. Before we move on, let us understand the justification leading to the inception of the big bang theory. This theory was proposed by a priest and astronomer named Georges LeMaître in the 1920s when scientists realized that the galaxies at the farthest points were moving away from us faster than the closest ones. This suggested the possibility that it’s not the galaxies that are moving, but the universe that’s expanding. From an expansion point of view, it is quite easy to visualize an expanding object to have been at its smallest at some point in time. The same was applied to the universe, rising the phenomenon of a singularity to have been the most probable starting point. Building on the theory of expansion, we understand that light stretches as well. The galaxies at the farthest end are red-shifted, meaning their light wavelengths have stretched out and headed for the red, lower-energy end of the electromagnetic spectrum. A very important conclusion that can be drawn from this is the fact that everything started out with higher energy in the past making the universe awfully hot at that point of time. Many examples exist in this very universe today that substantiate the same. To name a few, let us talk about the plasma soup that created the young universe. We also have a fairly good understanding of what those particles have merged into, which coincides with the exact ratio of particles we see in the universe today. We also see traces of proof in the form of the weak, super-stretched leftover radiation that makes up the cosmic microwave background. Everything seems to be falling into place, right? Well, not really, as is with anything to do with this mystery of a universe. Let us now dive into the deviations that question the accuracy of this theory. The cosmic microwave background proposes the idea that the universe is flat, which contradicts with the whole big bang expansion theory calling for the universe to be curved. Secondly, everything in the universe seems to about the same temperature. Finally, it is believed that the proposed big bang should have produced mega high-energy particles called magnetic monopoles but none of them has been found or traced yet. These deviations from the popular theory lead to the proposal of the inflation theory that discusses the birth of the universe to be a result of the fluctuations in the void of space. The basis behind this new theory is a quantity called vacuum energy. We understand that no matter of radiation existed before the big bang as per the inflation theory. That being said, a vacuum is still full of energy as a result of the pairs of quantum particles that constantly blink in and out of existence. This resultant energy led to the exponential expansion of the universe enlarging it by a factor close to 1026 in a fraction of a second. This expansion caused fluctuations in the vacuum energy leaving the fabric of space uneven. This essentially means that random spots existed where the energy density was slightly higher or slightly lower than average. Eventually, all that energy decayed into matter and radiation. The inflation theory fixes a lot of the holes in the big bang theory. It works with a flat universe and the rate at which it happened allows for uniformity in temperature (one of the variations in the big bang theory) as it suggests the possibility that every point in the universe might have once been in contact. Inflation also says that magnetic monopoles may have existed prior to expansion, but their density would have plummeted to insignificant levels afterwards. What’s more, the fluctuations in energy provide an excellent theory as to how galaxies and stars are formed. Humanity, as we know it today, came into spectacular existence due to those seemingly random clusters of energy, so before we look into the big bang as the mother of all existence, we might want to look closely into the hidden dawn of the universe.

The Big Bang Theory is the leading explanation about how the universe began. At its simplest, it says the universe as we know it started with a small singularity, then inflated over the next 13.8 billion years to the cosmos that we know today. Because current instruments don't allow astronomers to peer back at the universe's birth, much of what we understand about the Big Bang Theory comes from mathematical formulas and models. Astronomers can, however, see the "echo" of the expansion through a phenomenon known as the cosmic microwave background. While the majority of the astronomical community accepts the theory, there are some theorists who have alternative explanations besides the Big Bang — such as eternal inflation or an oscillating universe. The phrase "Big Bang Theory" has been popular among astrophysicists for decades, but it hit the mainstream in 2007 when a comedy show with the same name premiered on CBS. The show follows the home and academic life of several researchers (including an astrophysicist). The first second, and the birth of light In the first second after the universe began, the surrounding temperature was about 10 billion degrees Fahrenheit (5.5 billion Celsius), according to NASA. The cosmos contained a vast array of fundamental particles such as neutrons, electrons and protons. These decayed or combined as the universe got cooler. This early soup would have been impossible to look at, because light could not carry inside of it. "The free electrons would have caused light (photons) to scatter the way sunlight scatters from the water droplets in clouds," NASA stated. Over time, however, the free electrons met up with nuclei and created neutral atoms. This allowed light to shine through about 380,000 years after the Big Bang. This early light — sometimes called the "afterglow" of the Big Bang — is more properly known as the cosmic microwave background (CMB). It was first predicted by Ralph Alpher and other scientists in 1948, but was found only by accident almost 20 years later. [Images: Peering Back to the Big Bang & Early Universe] Arno Penzias and Robert Wilson, both of Bell Telephone Laboratories in Murray Hill, New Jersey, were building a radio receiver in 1965 and picking up higher-than-expected temperatures, according to NASA. At first, they thought the anomaly was due to pigeons and their dung, but even after cleaning up the mess and killing pigeons that tried to roost inside the antenna, the anomaly persisted. Simultaneously, a Princeton University team (led by Robert Dicke) was trying to find evidence of the CMB, and realized that Penzias and Wilson had stumbled upon it. The teams each published papers in the Astrophysical Journal in 1965. Determining the age of the universe The cosmic microwave background has been observed on many missions. One of the most famous space-faring missions was NASA's Cosmic Background Explorer (COBE) satellite, which mapped the sky in the 1990s. Several other missions have followed in COBE's footsteps, such as the BOOMERanG experiment (Balloon Observations of Millimetric Extragalactic Radiation and Geophysics), NASA's Wilkinson Microwave Anisotropy Probe (WMAP) and the European Space Agency's Planck satellite. Planck's observations, first released in 2013, mapped the background in unprecedented detail and revealed that the universe was older than previously thought: 13.82 billion years old, rather than 13.7 billion years old. [Related: How Old is the Universe?] (The research observatory's mission is ongoing and new maps of the CMB are released periodically.) The maps give rise to new mysteries, however, such as why the Southern Hemisphere appears slightly redder (warmer) than the Northern Hemisphere. The Big Bang Theory says that the CMB would be mostly the same, no matter where you look. Examining the CMB also gives astronomers clues as to the composition of the universe. Researchers think most of the cosmos is made up of matter and energy that cannot be "sensed" with conventional instruments, leading to the names dark matter and dark energy. Only 5 percent of the universe is made up of matter such as planets, stars and galaxies. Gravitational waves controversy While astronomers could see the universe's beginnings, they've also been seeking out proof of its rapid inflation. Theory says that in the first second after the universe was born, our cosmos ballooned faster than the speed of light. That, by the way, does not violate Albert Einstein's speed limit since he said that light is the maximum anything can travel within the universe. That did not apply to the inflation of the universe itself. In 2014, astronomers said they had found evidence in the CMB concerning "B-modes," a sort of polarization generated as the universe got bigger and created gravitational waves. The team spotted evidence of this using an Antarctic telescope called "Background Imaging of Cosmic Extragalactic Polarization", or BICEP2. "We're very confident that the signal that we're seeing is real, and it's on the sky," lead researcher John Kovac, of the Harvard-Smithsonian Center for Astrophysics, told Space.com in March 2014. But by June, the same team said that their findings could have been altered by galactic dust getting in the way of their field of view. "The basic takeaway has not changed; we have high confidence in our results," Kovac said in a press conference reported by the New York Times. "New information from Planck makes it look like pre-Planckian predictions of dust were too low," he added. The results from Planck were put online in pre-published form in September. By January 2015, researchers from both teams working together "confirmed that the Bicep signal was mostly, if not all, stardust," the New York Times said in another article. Separately, gravitational waves have been confirmed when talking about the movements and collisions of black holes that are a few tens of masses larger than our sun. These waves have been detected multiple times by the Laser Interferometer Gravitational-Wave Observatory (LIGO) since 2016. As LIGO becomes more sensitive, it is anticipated that discovering black hole-related gravitational waves will be a fairly frequent event. Faster inflation, multiverses and charting the start The universe is not only expanding, but getting faster as it inflates. This means that with time, nobody will be able to spot other galaxies from Earth, or any other vantage point within our galaxy. "We will see distant galaxies moving away from us, but their speed is increasing with time," Harvard University astronomer Avi Loeb said in a March 2014 Space.com article. "So, if you wait long enough, eventually, a distant galaxy will reach the speed of light. What that means is that even light won't be able to bridge the gap that's being opened between that galaxy and us. There's no way for extraterrestrials on that galaxy to communicate with us, to send any signals that will reach us, once their galaxy is moving faster than light relative to us." Some physicists also suggest that the universe we experience is just one of many. In the "multiverse" model, different universes would coexist with each other like bubbles lying side by side. The theory suggests that in that first big push of inflation, different parts of space-time grew at different rates. This could have carved off different sections — different universes — with potentially different laws of physics. "It's not impossible, so I think there's still certainly research that needs to be done. But most models of inflation do lead to a multiverse, and evidence for inflation will be pushing us in the direction of taking [the idea of a] multiverse seriously." While we can understand how the universe we see came to be, it's possible that the Big Bang was not the first inflationary period the universe experienced. Some scientists believe we live in a cosmos that goes through regular cycles of inflation and deflation, and that we just happen to be living in one of these phases.

Strange 'Methuselah' Star Looks Older Than the Universe The oldest known star appears to be older than the universe itself, but a new study is helping to clear up this seeming paradox. Previous research had estimated that the Milky Way galaxy's so-called "Methuselah star" is up to 16 billion years old. That's a problem, since most researchers agree that the Big Bang that created the universe occurred about 13.8 billion years ago. Now a team of astronomers has derived a new, less nonsensical age for the Methuselah star, incorporating information about its distance, brightness, composition and structure. "Put all of those ingredients together, and you get an age of 14.5 billion years, with a residual uncertainty that makes the star's age compatible with the age of the universe," study lead author Howard Bond, of Pennsylvania State University and the Space Telescope Science Institute in Baltimore, said in a statement. The uncertainty Bond refers to is plus or minus 800 million years, which means the star could actually be 13.7 billion years old — younger than the universe as it's currently understood, though just barely. A mysterious, fast-moving star Bond and his team used NASA's Hubble Space Telescope to study the Methuselah star, which is more formally known as HD 140283. Scientists have known about HD 140283 for more than 100 years, since it cruises across the sky at a relatively rapid clip. The star moves at about 800,000 mph (1.3 million km/h) and covers the width of the full moon in the sky every 1,500 years or so, researchers said. The star is just passing through the Earth's neck of the galactic woods and will eventually rocket back out to the Milky Way's halo, a population of ancient stars that surrounds the galaxy's familiar spiral disk. The Methuselah star, which is just now bloating into a red giant, was probably born in a dwarf galaxy that the nascent Milky Way gobbled up more than 12 billion years ago, researchers said. The star's long, looping orbit is likely a residue of that dramatic act of cannibalism. Distance makes the difference Hubble's measurements allowed the astronomers to refine the distance to HD 140283 using the principle of parallax, in which a change in an observers' position — in this case, Hubble's varying position in Earth orbit — translates into a shift in the apparent position of an object. They found that Methuselah lies 190.1 light-years away. With the star's distance known more precisely, the team was able to work out Methuselah's intrinsic brightness, a necessity for determining its age. The scientists also applied current theory to learn more about the Methuselah star's burn rate, composition and internal structure, which also shed light on its likely age. For example, HD 140283 has a relatively high oxygen-to-iron ratio, which brings the star's age down from some of the earlier predictions, researchers said. In the end, the astronomers estimated that HD 140283 was born 14.5 billion years ago, plus or minus 800 million years. Further observations could help bring the Methuselah star's age down even further, making it unequivocally younger than the universe, researchers said.

Of the myriad galaxies we've seen in the night sky, NGC 6240 has always stood out for its peculiar shape and unusual infrared brightness. It was thought to be the result of two galaxies colliding - until now. All the way back in 1983, astronomers reported evidence of a double active nucleus - two active supermassive black holes at the centre of NGC 6240. Now, for the first time, researchers have found evidence of a third supermassive black hole. This new finding suggests that not two, but three galaxies are in the process of merging, each bringing its own supermassive black hole galactic nucleus to the party. "Through our observations with extremely high spatial resolution," explained astrophysicist Wolfram Kollatschny from the University of Göttingen in Germany, "we were able to show that the interacting galaxy system NGC 6240 hosts not two - as previously assumed - but three supermassive black holes in its centre." Since 1983, numerous studies of the galaxy have been conducted, confirming that finding of two active galactic nuclei at the heart of NGC 6240, which lies 300 million light-years away as the photon flies. However, because the supermassive black holes are so close together, exactly where they are within the bright centre has remained elusive. Kollatschny and his team used the MUSE 3D spectrograph mounted on the European Southern Observatory's eight-metre Very Large Telescope in Chile to take high-resolution spectroscopic observations of the galaxy. These images revealed three nodes at the centre of NGC 6240 - one northern component and two southern. However, the new finding doesn't mean the previous research was wrong; the new evidence suggests that only two of the black holes are actively accreting matter, and the third is dormant. Each of the supermassive black holes clocks in at over 90 million times the mass of the Sun (the Milky Way's supermassive black hole, Sagittarius A*, is 4 million solar masses). All three are locked in an orbit in an area less than 1 kiloparsec across (3,260 light-years), slowly spiralling inward towards each other. And the two southern black holes are separated by a distance of just 198 parsecs (645 light-years). niverse," said astrophysicist Peter Weilbacher of the Leibniz Institute for Astrophysics Potsdam in Germany. "The present case provides evidence of a simultaneous merging process of three galaxies along with their central black holes." Earlier this year another triple merger was discovered, with three supermassive black holes in the process of inspiralling at the centre of a galaxy called SDSS J084905.51+111447.2; but that system had separations between each pair of black holes of around 10 kiloparsecs. That the black holes at the centre of NGC 6240 are closer to each other means NGC 6240 is in a later stage of its merger, a process that takes more than a billion years. This more advanced stage also means the galaxy is closer to what is known as the final parsec problem. As we have previously reported, according to theoretical modelling the black holes of two merging galaxies are inexorably drawn together, transferring their orbital energy to the gas and stars around them, and thus orbiting in an ever-tighter spiral. We know that pairs of stellar-mass black holes will eventually come together and form a single object. With supermassive black holes, there's a theoretical problem. As their orbit shrinks, so too does the region of space to which they can transfer energy. By the time they're one parsec apart (around 3.2 light-years), theoretically this region of space is no longer large enough to support further orbital decay, so they remain in a stable binary orbit - potentially for billions of years. This balance is known as the 'final parsec problem'. Triple mergers might be a solution to this problem, since the third black hole could provide the extra kick the objects need to close that final gap. Of course, the black holes at the centre of NGC 6240 won't get anywhere close to that final parsec any time soon - it could take another billion years or two, and who even knows if humanity will be around at that point. But the black holes are expected to be producing gravitational waves. We can't detect them yet, but by studying systems such as these, we may be able to figure out how to detect them with future instruments, and figure out what happens at that last parsec.

There’s a supermassive black hole – 4 million times our sun’s mass – in the center of our Milky Way galaxy. Astronomers who’ve measured star movements near this central black hole are now saying there might be a 2nd companion black hole near it. Do supermassive black holes have friends? The nature of galaxy formation suggests that the answer is yes, and in fact, pairs of supermassive black holes should be common in the universe. I am an astrophysicist and am interested in a wide range of theoretical problems in astrophysics, from the formation of the very first galaxies to the gravitational interactions of black holes, stars and even planets. Black holes are intriguing systems, and supermassive black holes and the dense stellar environments that surround them represent one of the most extreme places in our universe. The supermassive black hole that lurks at the center of our galaxy, called Sgr A*, has a mass of about 4 million times that of our sun. A black hole is a place in space where gravity is so strong that neither particles or light can escape from it. Surrounding Sgr A* is a dense cluster of stars. Precise measurements of the orbits of these stars allowed astronomers to confirm the existence of this supermassive black hole and to measure its mass. For more than 20 years, scientists have been monitoring the orbits of these stars around the supermassive black hole. Based on what we’ve seen, my colleagues and I show that if there is a friend there, it might be a second black hole nearby that is at least 100,000 times the mass of the sun. Supermassive black holes and their friends Almost every galaxy, including our Milky Way, has a supermassive black hole at its heart, with masses of millions to billions of times the mass of the sun. Astronomers are still studying why the heart of galaxies often hosts a supermassive black hole. One popular idea connects to the possibility that supermassive holes have friends. To understand this idea, we need to go back to when the universe was about 100 million years old, to the era of the very first galaxies. They were much smaller than today’s galaxies, about 10,000 or more times less massive than the Milky Way. Within these early galaxies the very first stars that died created black holes, of about tens to thousand the mass of the sun. These black holes sank to the center of gravity, the heart of their host galaxy. Since galaxies evolve by merging and colliding with one another, collisions between galaxies will result in supermassive black hole pairs – the key part of this story. The black holes then collide and grow in size as well. A black hole that is more than a million times the mass of our sun is considered supermassive. If indeed the supermassive black hole has a friend revolving around it in close orbit, the center of the galaxy is locked in a complex dance. The partners’ gravitational tugs will also exert its own pull on the nearby stars disturbing their orbits. The two supermassive black holes are orbiting each other, and at the same time, each is exerting its own pull on the stars around it. The gravitational forces from the black holes pull on these stars and make them change their orbit; in other words, after one revolution around the supermassive black hole pair, a star will not go exactly back to the point at which it began. Using our understanding of the gravitational interaction between the possible supermassive black hole pair and the surrounding stars, astronomers can predict what will happen to stars. Astrophysicists like my colleagues and me can compare our predictions to observations, and then can determine the possible orbits of stars and figure out whether the supermassive black hole has a companion that is exerting gravitational influence. Using a well-studied star, called S0-2, which orbits the supermassive black hole that lies at the center of the galaxy every 16 years, we can already rule out the idea that there is a second supermassive black hole with mass above 100,000 times the mass of the sun and farther than about 200 times the distance between the sun and the Earth. If there was such a companion, then I and my colleagues would have detected its effects on the orbit of SO-2. But that doesn’t mean that a smaller companion black hole cannot still hide there. Such an object may not alter the orbit of SO-2 in a way we can easily measure. The physics of supermassive black holes Supermassive black holes have gotten a lot of attention lately. In particular, the recent image of such a giant at the center of the galaxy M87 opened a new window to understanding the physics behind black holes. The proximity of the Milky Way’s galactic center – a mere 24,000 light-years away – provides a unique laboratory for addressing issues in the fundamental physics of supermassive black holes. For example, astrophysicists like myself would like to understand their impact on the central regions of galaxies and their role in galaxy formation and evolution. The detection of a pair of supermassive black holes in the galactic center would indicate that the Milky Way merged with another, possibly small, galaxy at some time in the past. That’s not all that monitoring the surrounding stars can tell us. Measurements of the star S0-2 allowed scientists to carry out a unique test of Einstein’s general theory of relativity. In May 2018, S0-2 zoomed past the supermassive black hole at a distance of only about 130 times the Earth’s distance from the sun. According to Einstein’s theory, the wavelength of light emitted by the star should stretch as it climbs from the deep gravitational well of the supermassive black hole. The stretching wavelength that Einstein predicted – which makes the star appear redder – was detected and proves that the theory of general relativity accurately describes the physics in this extreme gravitational zone. I am eagerly awaiting the second closest approach of S0-2, which will occur in about 16 years, because astrophysicists like myself will be able to test more of Einstein’s predictions about general relativity, including the change of the orientation of the stars’ elongated orbit. But if the supermassive black hole has a partner, this could alter the expected result. Finally, if there are two massive black holes orbiting each other at the galactic center, as my team suggests is possible, they will emit gravitational waves. Since 2015, the LIGO-Virgo observatories have been detecting gravitational wave radiation from merging stellar-mass black holes and neutron stars. These groundbreaking detections have opened a new way for scientists to sense the universe. Any waves emitted by our hypothetical black hole pair will be at low frequencies, too low for the LIGO-Virgo detectors to sense. But a planned space-based detector known as LISA may be able to detect these waves, which will help astrophysicists figure out whether our galactic center black hole is alone or has a partner. Smadar Naoz, Associate Professor of Physics & Astronomy, University of California, Los Angeles This article is republished from The Conversation under a Creative Commons license. Read the original article. Bottom line: Measurements of star orbits near the massive black hole in the center of the Milky Way galaxy suggest that there may be a second companion black hole nearby.

Were you wondering what galaxy is the Earth in? You’ll probably recognize the answer: it’s the Milky Way Galaxy. If you go to a dark spot, away from the bright city lights, and look up, you should be able to see the Milky Way as a cloudy band stretching across the sky. It really does look like spilt milk spread across the sky. But if you take a telescope and examine it more closely, you’ll see that the clouds are actually the collective light from thousands of stars. Since we’re embedded inside the Milky Way, we’re seeing our home galaxy edge-on, from the inside. To get a better idea, grab a dinner plate and take a look at it edge on, so you can’t see the circular shape of the galaxy. You can only see the edge of the plate. The Milky Way is an example of a barred spiral galaxy. It measures approximately 100,000 light years across and it’s only 1,000 light years thick; although, it’s more thick at the core where the galaxy bulges out. If you could fly out of the Milky Way in a rocket and then look back, you’d see a huge spiral shaped galaxy with a bar at the center. At the ends of this bar, there are two spiral arms which twist out forming the structure of the Milky Way. The Earth is located in the Solar System, and the Solar System is located about 25,000 light-years away from the core of the galaxy. This also means that we’re about 25,000 light-years away from the outer edge of the Milky Way. We’re located in the Orion Spur, which is a minor arm located in between the two major galactic arms.