Wormholes are theoretical tunnels through the fabric of space-time that could potentially allow rapid travel between widely separated points — from one galaxy to another, for example, as depicted in Christopher Nolan’s “Interstellar,” which opened in theaters around the world earlier this month.
While wormholes are possible according to Einstein’s theory of general relativity, such exotic voyages will likely remain in the realm of science fiction, said renowned astrophysicist Kip Thorne of the California Institute of Technology in Pasadena, who served as an adviser and executive producer on “Interstellar.”
“The jury is not in, so we just don’t know,” Thorne, one of the world’s leading authorities on relativity, black holes and wormholes, told Space.com. “But there are very strong indications that wormholes that a human could travel through are forbidden by the laws of physics. That’s sad, that’s unfortunate, but that’s the direction in which things are pointing.”
The major barrier has to do with a wormhole’s instability, he said.
“Wormholes — if you don’t have something threading through them to hold them open — the walls will basically collapse so fast that nothing can go through them,” Thorne said.
Holding wormholes open would require the insertion of something that anti-gravitates — namely, negative energy. Negative energy has been created in the lab via quantum effects, Thorne said: One region of space borrows energy from another region that didn’t have any to begin with, creating a deficit.
“So it does happen in physics,” he said. “But we have very strong, but not firm, indications that you can never get enough negative energy that repels and keeps the wormhole’s walls open; you can never get enough to do that.”
Furthermore, traversable wormholes — if they can exist at all — almost certainly cannot occur naturally, Thorne added. That is, they must be created by an advanced civilization.
And that’s exactly what happens in “Interstellar”: Mysterious beings construct a wormhole near Saturn, allowing a small band of pioneers, led by a former farmer named Cooper (played by Matthew McConaughey) to journey far afield in search of a new home for humanity, whose existence on Earth is threatened by global crop failures.
Anyone interested in learning more about the science of “Interstellar” — which also features gravitational time dilation and depictions of several alien planets orbiting close to a supermassive black hole — can check out Thorne’s new book, which is called, appropriately enough, “The Science of ‘Interstellar.’”
Wormholes have been a staple of science fiction for decades. Interestingly, Thorne said that one of the genre’s most famous titles helped inspire scientists to try to better understand the hypothetical structures.
“The modern research on the physics of wormholes largely stems from the movie ‘Contact,’ from conversations I had with [renowned late scientist] Carl Sagan — actually, when he was writing his novel ‘Contact,’” Thorne said.
“Contact” features traversable wormholes. The novel came out in 1985, while the movie (which also stars Matthew McConaughey, apparently a wormhole connoisseur) was released in 1997.
Astronomers using a NASA space telescope are in the midst of a survey designed to figure out how galaxies in the young universe grew so quickly.
The first results from the project, which used the Spitzer Space Telescope, show hundreds of huge galaxies (100 times the mass of the Milky Way) that were around when the 13.8-billion-year-old universe was in its cosmic infancy.
This presents a dilemma for astronomers, who are hard-pressed to explain how such behemoths came to be so early in the universe’s history. Spitzer is about to embark on a three-month examination to hunt dim galaxies that are billions of light-years from Earth. [Read the latest news about galaxies and stars]
“If you think of our survey as fishing for galaxies in the cosmic sea, then we are finding many more big fish in deep waters than previously expected,” lead author Charles Steinhardt, of NASA’s Infrared Processing and Analysis Center (IPAC) at the California Institute of Technology in Pasadena, said in a statement.
The project is dubbed SPLASH (short for Spitzer Large Area Survey with Hyper-Suprime-Cam). Researchers aim to use the telescope for 2,475 hours to look at two dark areas of the sky, far away from the Milky Way’s field of stars.
The fields, which have been examined before, are called the Cosmic Evolution Survey (COSMOS) and Subaru/XMM-Newton deep field (SXDS). Each sky area is about the size of eight full moons. Spitzer’s examination in infrared wavelengths will help astronomers see the masses of these galaxies.
Star formation models now postulate that the earliest galaxies crashed into each other and as they came together, grew larger and encouraged starbirth. However, this process would not work fast enough (as far as astronomers understand) to create the huge galaxies Spitzer is seeing between 800 million and 1.6 billion years after the universe was formed.
Perhaps the first galaxies came into existence than scientists thought. While many astronomers believe galaxies began growing about 500 million years after the Big Bang that formed the universe, the growth rate works if this process started at 400 million years. But there are other theories as well.
“It’s really hard to form something so massive so quickly,” Josh Speagle, co-author of the study from Harvard University in Massachusetts, said in the same statement. “So it’s entirely possible that these galaxies have been forming stars continuously since the moment they were born.”
Scientists will take a closer look at these galaxies using the Subaru telescope in Hawaii, which will do several years of observations to follow up on what Spitzer found.
The large project is possible with Spitzer because it is past its prime mission; its coolant ran out in 2009, meaning some of its instruments don’t work. The telescope, however, is still able to work in two infrared channels despite being warmer, and now looks at bigger areas of the sky for longer.
The photo, taken by Spitzer observatory in infrared light, shows a burst of starbirth in the galaxy NGC 1291, which lies 33 million light-years from Earth and is about 12 billion years old. Older stars are colored blue in the photo and cluster mostly in the central region of the galaxy; younger, red stars appear around the fringes.
“The rest of the galaxy is done maturing,” said lead researcher Kartik Sheth, of the National Radio Astronomy Observatory of Virginia, in a statement. “But the outer ring is just now starting to light up with stars.”
The image was captured as part of a study on structural features in barred galaxies, so called because they have a long central bar of stars within them. The Milky Way is an example of a barred spiral galaxy.
Astronomers believe NGC 1291′s bar was created when the galaxy was young. The bar moves material through the galaxy, shifting stars and gas into noncircular orbits. In some places, galactic gas is pushed together, where it collapses to form stars, researchers said.
Scientists believe that early in a galaxy’s history, the bars push gas into the center and spark starbirth there. As the galaxy ages, the fuel depletes and stars are born farther and farther from the core.
Spitzer survey aims to discover more about how barred galaxies form and evolve, which could shed light on the conditions that created the Milky Way, among other things.
“Now, with Spitzer we can measure the precise shape and distribution of matter within the bar structures,” Sheth said. “The bars are a natural product of cosmic evolution, and they are part of the galaxies’ endoskeleton. Examining this endoskeleton for the fossilized clues to their past gives us a unique view of their evolution.”
That question will took center stage during a debate on Oct. 16 at 7:30 p.m. EDT (2330 GMT) organized by the Harvard-Smithsonian Center for Astrophysics (CfA). You can watch the event live here on Space.com, courtesy of the CfA, or on the CfA’s “Observatory Nights” YouTube channel: http://www.youtube.com/user/ObsNights
Two CfA researchers will participate in tonight’s debate, CfA representatives wrote in a media advisory:
“Ofer Cohen will discuss the latest research suggesting that harsh winds and stellar radiation would scour any planets in the habitable zone. Elisabeth Newton will argue that red dwarf worlds could be more resilient than we think.”
Astronomers have discovered nearly 2,000 alien planets to date, and they’ve only scratched the surface: Each one of the Milky Way’s 100 billion or so stars is believed to host more than one planet on average.
The new image of the Spiderweb Galaxy (also known as MRC 1138-262) shows blobs of dust that are actually galaxies, captured by a European Southern Observatory telescope in Chile. The entire galaxy cluster surrounds a radio galaxy that has a supermassive black hole at its center.
Here’s where the surprise came: Scientists discovered that 10 billion years ago, star formation was happening mostly in one spot that wasn’t at the center of the galaxy complex. Astronomers instead thought star formation would happen in the filaments of the cluster. Why is unclear.
“We aimed to find the hidden star formation in the Spiderweb cluster — and succeeded — but we unearthed a new mystery in the process; it was not where we expected,” lead researcher Helmut Dannerbauer, a post-doctoral galaxy researcher at the University of Vienna, Austria, said in a statement. “The mega city is developing asymmetrically.”
Galaxy clusters are the largest structures in the universe, but their formation and evolution is poorly understood.
The image was captured using the ESO’s Atacama Pathfinder Experiment telescope (APEX) telescope in Chile.
APEX examined the galaxy cluster in submillimeter wavelengths designed to penetrate dust. Across 40 hours of observations, the researchers found four times as many sources of star formation than previously known.
This is one of the deepest observations ever made with APEX and pushes the technology to its limits – as well as the endurance of the staff working at the high-altitude APEX site,” Carlos De Breuck, a co-author on the study who is the APEX project scientist at ESO said in the same statement.
These starbirth hubs are happening at the same distance as the cluster itself, according to observations using other wavelengths of light, which shows the star-formation regions must be part of the cluster.
For years, mysterious dark matter has eluded scientists, and now, a new study shows there may be less of it to find.
Using a century-old equation, scientists have found that the Milky Way galaxy holds half as much dark matter — the invisible stuff believed to make up a sizable chunk of the universe — as scientists had previously thought.
By calculating the speed of stars throughout the galaxy and conducting a detailed study of the Milky Way’s outer edges, a team of astronomers in Australia determined that the amount of the unseen dark matter in the galaxy is just 80 billion times the mass of the sun — half the mass of recent estimates.
In the 1950s, scientists determined that galaxies contain more matter than the human eye can see. The everyday material humans can see is made of baryonic matter, and it contains protons, neutrons and electrons. Scientists think dark matter may be composed of baryonic matter, nonbaryonic matter or a mixture of the two. Several possibilities for the material have been raised in recent years.
“Stars, dust, you and me — all the things that we see — only make up about 4 percent of the entire universe,” study lead author Prajwal Kafle, from the University of Western Australia, said in a statement. “About 25 percent is dark matter, and the rest is dark energy.”
Kafle and his team utilized the most up-to-date measurements of the galaxy. The measurements of the outer edges of the galaxy included more detailed studies than previous observations had. Then, the team used a technique developed by British astronomer James Jeans in 1915, long before researchers had envisioned dark matter.
In determining that the Milky Way contains less dark matter than previously thought, Kafle and his fellow researchers gained insight into a problem that theorists have been struggling with for almost 20 years.
“The current idea of galaxy formation and evolution, called the Lambda Cold Dark Matter Theory, predicts that there should be a handful of big satellite galaxies around the Milky Way that are visible with the naked eye, but we don’t see that,” Kafle said. “When you use our measurement of the mass of the dark matter, the theory predicts that there should only be three satellite galaxies out there, which is exactly what we see — the Large Magellanic Cloud, the Small Magellanic Cloud and the Sagittarius Dwarf [Spheroidal] galaxy.”
Multiple telescopes on the ground and in space gathered information on Sparky, which is more formally known as GOODS-N-774. The half-built galaxy lies 11 billion light-years from Earth, so viewing it gives astronomers a glimpse into processes that occurred less than 3 billion years after the Big Bang that created the universe.
“It’s a formation process that can’t happen anymore,” study lead author Erica Nelson, a graduate student at Yale University in Connecticut, said in a statement. “The early universe could make these galaxies, but the modern universe can’t. It was this hotter, more turbulent place.”
The dramatic starscape confirms a longstanding theory that huge elliptical galaxies form core-first, researchers said. Elliptical galaxies — the most numerous type in the universe — are primarily composed of older stars and generally have little gas left in them.
Astronomers first looked at Sparky with an infrared camera on NASA’s Hubble Space Telescope, then examined the galaxy by looking at archival images from the agency’s Spitzer Space Telescope and Europe’s Herschel Space Observatory, which ceased operations in 2013.
The various observations revealed that Sparky is creating about 300 stars per year, more than 30 times the rate in Earth’s own Milky Way galaxy. Sparky’s prolific nature is even more impressive considering its diminutive size; the galaxy is only about 6,000 light-years across, compared to the Milky Way’s 100,000 light-years.
Astronomers got more details about Sparky’s formation using a near-infrared spectrograph on the Keck Observatory in Hawaii. Keck revealed gas clouds quickly orbiting around the galaxy’s center, providing the material needed to create young stars.
Further, a thick layer of dust covers the galaxy, so even more stars could be forming while remaining unseen, researchers said.
“It’s like a medieval cauldron forging stars. There’s a lot of turbulence, and it’s bubbling,” Nelson said. “If you were in there, the night sky would be bright with young stars, and there would be a lot of dust, gas and remnants of exploding stars. To actually see this happening is fascinating.”
The stellar baby boom was likely fueled by a huge stream of gas flowing into the galactic core, which houses a substantial amount of dark matter, a mysterious substance believed to form the backbone of galaxies.
The next goal is to find out how often this sort of situation occurred in the early universe. Astronomers said learning such details will likely require more-sensitive infrared telescopes, such as NASA’s $8.8 billion James Webb Space Telescope, which is scheduled to launch in 2018.
A paper on the research was published in the Aug. 27 edition of the journal Nature.
If you point a telescope near the constellations of Leo and Virgo, you might be able to catch a glimpse of the galactic monster in question: the Umbrella Galaxy, formally called NGC 4651.
This spiral galaxy — a twin of the Milky Way — is eating a smaller galaxy, and it gets its whimsical nickname from the wispy “parasol” that surrounds it.
When scientists discovered this umbrella in the 1950s, they interpreted it as a dwarf galaxy companion to the bigger galaxy. But recent research has suggested this parasol might actually be made up of crumbs from a leftover meal.
Astronomers have shown that our own Milky Way has fattened up by acquiring stars from other, smaller galaxies. They’ve found streams of star crumbs emanating from the nearby Sagittarius dwarf galaxy, which is being engulfed by the Milky Way.
What’s more, a study in 2010 that looked at eight spiral galaxies, including the Umbrella Galaxy, found that six of them had signs of mergers: shells, clouds and arcs of tidal debris.
Researchers led by Caroline Foster of the Australian Astronomical Observatory (AAO) have been studying the Umbrella Galaxy, and they learned that its distinctive arc is made up of the crumbs from a single dinner, rather than a series of meals.
“Through new techniques we have been able to measure the movements of the stars in the very distant, very faint, stellar stream in the Umbrella,” Foster explained in a statement from the AAO. “This allows us to reconstruct the history of the system, which we couldn’t before.”
The astronomers used observations from the Subaru and Keck telescopes in Hawaii, and they tracked the movement of the stars in the stream by looking at globular clusters, planetary nebulae and patches of hydrogen gas in the galaxy. (Its distance from Earth is not well established, but the researchers in the study estimated that it is 62 million light-years away.)
The study, which has been accepted for publication in the Monthly Notices of the Royal Astronomical Society, is free to read online at the preprint service arxiv.
Brilliant bursts of star formation in distant dwarf galaxies seen by NASA’s Hubble Space Telescope could reveal new information about the early history of the universe, scientists say.
Galaxies churn out new stars all the time, but most of the universe’s stars formed between two and six billion years after the Big Bang (which occurred 13.8 billion years ago). The new Hubble observations capture the prolific dwarf galaxies, which are known as “starburst galaxies,” during this dramatic epoch, researchers said. You can watch a video explaining the new dwarf galaxy observations .
“We already suspected that dwarf starbursting galaxies would contribute to the early wave of star formation, but this is the first time we’ve been able to measure the effect they actually had,”study lead author Hakim Atek, of the École Polytechnique Federale de Lausanne in Switzerland, said in a statement.
“They appear to have had a surprisingly significant role to play during the epoch where the universe formed most of its stars,” Atek added.
The distant dwarf galaxiesthat the Hubble telescope observed are forming stars so quickly that they can double the number of stars they hold in just 150 million years. Normal galaxies take 1 to 3 billion years to do this, researchers said.
Starburst galaxies are relatively rare; researchers think these galaxies generally require a powerful event, such as a supernova explosion or galaxy merger, to get kicked into star-forming gear.
Hubble observed the dwarf galaxies using its Wide Field Camera 3 (WFC3) instrument, which captures images in a wide range of wavelengths. In the new study, infrared light proved key to illuminating the faraway starburst galaxies.
WFC3 also has a prism, which splits light into its constituent wavelengths. The spectroscopy mode of the camera produced the images, in which each galaxy appears as a rainbow streak. Scientists analyze the galaxies’ spectra to estimate how far away they are from Earth and determine their chemical composition.
Previous studies of starburst galaxies had focused on nearby or large galaxies, leaving out the faraway, ancient dwarfs, which are more difficult to observe, researchers said.
The iconic Hubble Space Telescope has been snapping pictures of the universe since 1990 and is part of NASA’s “Great Observatories” project.
The universe is expanding — and it is doing so at the same rate in all directions, according to new measurements that appear to confirm the standard model of cosmology.
Astrophysicist Jeremy Darling of the University of Colorado Boulder came to this conclusion after employing a research strategy known as “real-time cosmology,” which seeks out the tiny changes in the universe that occur over human timescales.
The idea of “real-time cosmology” was proposed in two separate papers by Alan Sandage in 1962 and by Harvard astrophysicist Avi Loebin 1998. The possibility of seeing the redshifts of sources changing in real time is thus called the “Sandage-Loeb Test”. [The Universe: Big Bang to Now in 10 Easy Steps]
“Real-time cosmology offers new ways to observe the universe, including some observations and cosmological tests that cannot be made any other way,” Darling told Space.com via email.
Researchers discovered in 1998 that the universe is expanding at an accelerating rate — a surprising phenomenon believed to be due to a mysterious force called dark energy. Scientists don’t know much about dark energy, except that it may be a property of the vacuum. In a bid to understand dark energy, researchers are making a wide array of cosmological tests and building new telescopes and instruments.
“This work asks whether the expansion today — that is dominated by dark energy — is the same in all directions,” Darling said.
To make the measurements, Darling used data previously collected by other researchers on the motion of extra-galactic objects across the sky.
The data allowed him to conclude that the cosmic expansion is indeed isotropic — in other words, the same in all directions — with a margin of error of 7 percent.
“The constraints will get better with forthcoming data from the Gaia mission,” said Loeb, who was not involved in the study.
The European Space Agency’s Gaia probe, which launched last December, is designed to create a three-dimensional map of Earth’s Milky Way galaxy, mapping the motions of about 1 billion objects. This work should dramatically expand the sample size currently available to Darling and other researchers.
Traditionally, most cosmological observations treat the universe as frozen in time: with a fixed age, fixed distances and fixed properties. So, to see the history of the universe, scientists must look at similar objects at different distances.
Since the speed of light is finite, observers see more-distant objects as they existed at earlier cosmological times. The traditional strategy is thus to develop a statistical sample of cosmological “probes” across time to study how everything in the universe changes and evolves.
There is one exception to this statistical approach, though: the cosmic microwave background (CMB), the so-called “first light” left over from the Big Bang that created the universe 13.8 billion years ago.
“It arises from a single time that shows a fairly complete snapshot of the universe at that instant,” Darling said. “But the CMB is also treated as static.” [Cosmic Microwave Background: Big Bang Relic Explained (Infographic)]
Real-time cosmology, however, takes a different tack, relying on the idea that “now” is a changing time.
“If we lived long enough, we would see objects receding away from us, growing smaller and fainter with distance, and accelerating,” Darling said. “We would see the CMB roiling as new parts of the last scattering surface — the light horizon — receded. We would see gravity at work, causing large structures of galaxies and galaxy clusters to collapse and voids to expand.
“Basically, any observable property should change in real time if we could watch for a very long time, or [if] we could measure things (positions, velocities) extremely precisely.”
Real-time cosmology measurements are “raw” observations that don’t rely on models or statistical samples.
“I could pick my favorite galaxy and watch it accelerate, shrink and dim as it recedes, directly revealing the dynamic aspect of the universe,” Darling said.
And, he added, real-time cosmology could help find answers to the most basic but important questions about the cosmos, such as whether or not the universe is rotating, the nature of dark energy and the masses of large-scale structures in the universe.
While future instruments should give real-time cosmology a big boost, it’s already possible to make major discoveries using this strategy, Darling said.
“Precision astrometry — measuring the position of objects in the sky — can be done now both at radio wavelengths, with very long baseline interferometry, especially the Very Long Baseline Array, and optical wavelengths — the Gaia mission,” he said. “The acceleration can be directly measured with 30-meter [98 feet] optical telescopes and with the future radio Square Kilometer Array [in Australian and South Africa].” [10 Biggest Telescopes on Earth: How They Measure Up]
And, he added, the International Celestial Reference Frame data already offer an early way to test the models and theories of real-time cosmology. The ICRF is the framework researchers use to calibrate their measurements of where objects are in the sky.
“It is used to monitor the Earth’s rotation and its wobbles and glitches,” said Darling. “A network of radio-bright quasars are monitored regularly using very long baseline interferometry, and have been for decades. The measurements of the positions of these quasars are so precise that they can be used for all sorts of ancillary science.”
There are certain limitations, though — such as precision in redshift and astrometry, and the systematic errors associated with precise measurement.
“Accelerations are expected to be less than 1 centimeter per second per year, and astrometry needs to be about 1 microarcsecond per year,” Darling said. “The next step is to reach the limit of current VLBI [very-long-baseline interferometry] and then start using Gaia, which is likely to happen in three to five years.”
Loeb calls the work “original and interesting.” However, he says, “within the broader context of cosmological data, one can use the cosmic microwave background to conclude that the expansion is isotropic to better than 0.001 percent, or else we would see temperature variations across the sky that are larger than observed.”
Darling acknowledges that this is true, but argues that the CMB temperature as observed depends only on the total amount of expansion that occurred between when the light was emitted and when it was observed.
“It cannot be used to measure the expansion rate today (or at any other time),” Darling said. “It can, however, tell us about the overall, history-integrated anisotropy (i.e., did the universe grow more in one dimension than another since it was 300,000 years old, making one part of the sky appear colder/redder than another).”
Most importantly, Darling said, real-time cosmology allows researchers to make “new measurements of the universe to test our theoretical understanding. This is how new discoveries are made. It is good to see that the universe as observed today behaves itself and supports the current cosmological paradigm and causes no conflict with the CMB.”
His research has been accepted for publication in the journal Monthly Notices of the Royal Astronomical Society.
But author and astrophysicist Jeffrey Bennett believes relativity should be something anyone can understand. He explains what relativity is and how it causes a slew of bizarre effects in his new book, “What is Relativity?” (Columbia University Press, 2014).
In an excerpt from the book’s first chapter, Bennett takes readers on a voyage to a black hole, a mysterious realm in which the full strangeness of relativity is on display.
Part 1: Introduction
Chapter 1: Voyage to a Black Hole
Imagine that the sun magically collapsed, retaining the same mass but shrinking in size so much that it became a black hole. What would happen to Earth and the other planets? Ask almost anyone, including elementary school kids, and they’ll tell you confidently that the planets “would be sucked in.”
Now imagine that you’re a future interstellar traveler. Suddenly, you discover that a black hole lurks off to your left. What should you do? Again, ask around, and you’ll probably be told to fire up your engines to try to get away, and that you’ll be lucky to avoid being “sucked into oblivion.”
But I’ll let you in on a little secret that’s actually important to understanding relativity: Black holes don’t suck. If the sun suddenly became a black hole, Earth would become very cold and dark. However, since we’ve assumed that the black hole will have the same mass as the sun, Earth’s orbit would hardly be affected at all.
As for your future as an interstellar traveler… First of all, you wouldn’t “suddenly” discover a black hole off to your left. We have ways to detect many black holes even from Earth, and if we are someday able to embark on interstellar trips we’ll surely have maps that would alert you to the locations of any black holes along your route. Even in the unlikely event that one wasn’t on your map, the black hole’s gravitational effect on your spacecraft would build gradually as you approached, so there’d still be nothing sudden about it. Second, unless you happened to be aimed almost directly at the black hole, its gravity would simply cause you to swing around it in much the same way that we’ve sent spacecraft (such as the Voyager and New Horizons spacecraft) swinging past Jupiter on trips to the outer solar system.
I realize that this may be very disappointing to some of you. As my middle-school daughter put it, “but it’s cool to think that black holes suck.” I was able to placate her only somewhat by pointing out that being cool and “it sucks” don’t usually go together. Still, you’re probably wondering, if black holes don’t suck, what do they do?
The answer has two parts, one mundane and one so utterly amazing that you’ll never again miss your visions of a cosmic vacuum cleaner. The mundane part applies to black holes observed from afar, because at a distance the gravity of a black hole is no different than the gravity of any other object. That’s why turning the sun into a black hole would not affect Earth’s orbit, and why a spacecraft can swing by a black hole just like it swings by Jupiter. The amazing part comes when you begin to approach a black hole closely. There, you’d begin to observe the dramatic distortions of space and time that we can understand only through Einstein’s theory of relativity.
That brings us to the crux of the matter. I’ve begun this book on relativity by talking about black holes because, although almost everyone has heard of them, you cannot actually understand what black holes are unless you first understand the basic ideas discovered by Einstein. One goal of this book is to help you gain that understanding. But I have a second, more important goal in mind as well.
In the process of learning about relativity, you’ll find that your everyday notions of time and space do not accurately reflect the reality of the universe. In essence, you’ll realize that you have grown up with a “common sense” that isn’t quite as sensible as it seems. It’s not your fault; rather, it is a result of the fact that we don’t commonly experience the extreme conditions under which the true nature of time and space is most clearly revealed. Therefore, the real goal of this book is to help you distinguish reality from the fiction that we grow up with, and in the process to consider some of the profound implications of this reality that Einstein was the first to understand.
To get started, let’s take an imaginary voyage to a black hole. This journey will give you an opportunity to experience the two conditions under which Einstein’s ideas have their most dramatic effects: at speeds approaching the speed of light and in the extreme gravity that exists near black holes. For now, we’ll focus only on what you actually observe on your trip, saving the why that lies behind your observations for the chapters that follow.
Astronomers are one step closer to solving a longstanding mystery — just what our Milky Way galaxy looks like.
It may seem odd that a comprehensive understanding of the Milky Way’s structure has so far eluded researchers. But it’s tough to get a broad view of the galaxy from within.
“We are fairly confident that the Milky Way is a spiral galaxy, but we don’t know much in detail. At the most basic level, we’d like to be able to make a map that would show in detail what it looks like,” said Mark Reid of the Harvard-Smithsonian Center for Astrophysics, who led the new study. [Stunning Photos of Our Milky Way Galaxy (Gallery)]
Using the Very Long Baseline Array (VLBA), a system of 10 radio telescopes spanning the globe from Hawaii to New England to the Virgin Islands, and operated in Socorro, N.M., Reid’s team studied masers — naturally occurring sources of laser-like radio waves from clouds of gas near luminous stars — to map our galaxy in unprecedented detail.
“Mark Reid’s paper presents the most precise data we have on the dynamics and structure of the Milky Way galaxy,” said Harvard theorist Avi Loeb, who did not take part in the study.
Previous studies of the Milky Way’s structure were limited to nearby stars or relied on inferring distances from measurements of the speed of gas clouds approaching or receding from us. But these techniques are not reliable enough to discern the finer points of the Milky Way’s structure. So Reid’s team decided to go one step further.
The researchers first tried to get precise values of the Milky Way’s most fundamental parameters — the distance to the galactic center and the speed with which our sun rotates around it. These parameters directly relate to the size and total mass of the Milky Way.
To do so, they measured parallax — an effect that reflects the apparent position of an object when viewed from two different vantage points. This is essentially the same technique used for surveying on Earth, only carried to extraordinary accuracy with the VLBA.
“Were the human eye to have this accuracy, one could see individual molecules in one’s hand,” Reid said.
Astronomers measure parallax by observing how stars appear to move back and forth as the Earth orbits the sun. Using this technique, Reid’s team first measured the position of a bright maser spot coming from a dense cloud surrounding a newly formed and massive star.
Six months later, the astronomers measured the position again, when the Earth had moved halfway around the sun.
“This gives us two different vantage points, and the bright spot will appear to have moved by a small angle on the sky between the two observations,” said Reid.
Then they made a third measurement, when the Earth returned to its original position, to account for the motions of the sun and the target object. “Knowing the Earth-sun distance and the change in angle allows us to calculate the distance to the starby simple trigonometry,” Reid said.
The results have been impressive. As Reid and his colleagues describe in the paper, published this month in The Astrophysical Journal, it has been possible to determine the location of bright young stars that trace spiral structures in our galaxy, and even to measure how tightly wound the Milky Way’s spiral arms are.
“A typical spiral arm starts near the center of the Milky Way and wraps around once before fading away for lack of material to form stars,” Reid said.
But Loeb said that the most important results of the recent study were the much more accurate estimates of the distance to the galactic center and the circular rotation speed at the sun’s location.
“These values are of fundamental importance to many other studies of the Milky Way,” Loeb said.
Together with Gaia
Since the VLBA is in the Northern Hemisphere, it can only “see” about half of the Milky Way. So the next step is to take the same measurements in the Southern Hemisphere.
Once that’s done, Reid is confident that it should be possible to trace the Milky Way’s arms from their origin in the inner regions of the galaxy around to the outer parts.
His team’s ground-based observations will soon be greatly extended by the European Space Agency’s Gaia spacecraft, which launched in December. Gaia aims to measure the distances to one billion stars by about 2020. [Photos: Gaia Spacecraft to Map Milky Way Galaxy]
“Gaia is an optical telescope and cannot peer through the dusty plane of the Milky Way, where spiral structures dominate, whereas the VLBA uses radio waves that are unaffected by dust,” Reid said, “so the two approaches are quite complementary.”
Instead of measuring parallax distances and mapping the Milky Way, an alternative would be to design a space probe that could move at nearly the speed of light, Reid said.
“In about 10,000 years it would get out of the Milky Way and could take a picture and send it back to us and we would know what the Milky Way looks like,” he said. “Of course it would take another 10,000 years to transmit the image back to us. I’d like to know the answer sooner.”
You can read the paper at the online preprint site ArXiv here: http://xxx.lanl.gov/abs/1401.5377
The Atacama Large Millimeter/submillimeter Array (ALMA) is a telescope array in Chile that includes 66 receivers scattered across the Atacama Desert. The array is located at the European Southern Observatory and bills itself as “the largest astronomical project in existence.”
ALMA is able to peer through the dust that obscures planetary systems under construction, or to look back at stars and galaxies that formed in the early days of the universe and emit their radiation in millimeter light — waves that are about 1,000 times longer than visible-light wavelengths.
Although there are other observatories that can do the same thing, what distinguishes ALMA is its sheer size and number of receivers. Working together, they provide more sensitivity in astronomical observations and allow astronomers to look at the universe in high definition.
ALMA can be viewed as an amalgamation of three separate projects under conception: the Millimeter Array (MMA) of the United States, the Large Southern Array (LSA) of Europe and the Large Millimeter Array (LMA) of Japan. Through conversations between researchers, scientists concluded it would be easier to collaborate on one large project rather than creating several smaller ones.
The first large milestone occurred in 1997, when the European Southern Observatory (ESO) and the National Radio Astronomy Observatory (NRAO) agreed to merge MMA and LSA, a move they formalized in 1999. The ALMA agreement between the entities was subsequently signed in February 2003, with Japan joining in 2004.
ESO — which already has facilities in Chile — negotiated an agreement with the country to build ALMA at Llano de Chajnantor, a high-altitude site that would make it easier to observe the cosmos because the atmosphere is thinner there. In exchange, Chile received 10 percent observing time and additional “cultural, educational and production activities,” according to ALMA. The $1.3 billion cost was borne principally by North America and Europe, with Japan close behind.
Contracts for the antennas were awarded in 2005, with the first antenna coming to Chile in 2007. As antennas arrived and were checked for health and interferometry capabilities, ESO put out a call for the first science observations. Antennas began moving to Chajnantor in 2009, and observations began with a partially completed ALMA in 2011. The 66th and final receiver was installed in 2013.
ALMA’s extreme altitude is an aid in performing observations. Its highest receivers are about 16,500 feet (5,000 meters) above sea level, far above much of the atmosphere and water vapor that can make it hard to see what’s in the sky. Astronomers work in a facility at 9,500 feet (2,900 m), where they receive supplemental oxygen if they’re going to stay awhile.
The 66 receivers can be arranged in many different configurations, ranging from very close together to quite spread apart. At its greatest, the receivers can be moved as far as 9.9 miles (16 kilometers) apart. Each telescope receives information individually, then transmits the data to a supercomputer that combines the information to trace the signal direction — a high-tech version of how human ears combine to locate a sound.
This technology allows astronomers to look at three principal questions, according to ALMA’s website: the nature of the universe’s first stars and galaxies, how planets and stars come together, and what the chemistry is of the gas and dust clouds that may eventually collapse to form planets and stars.
“Many other astronomical specialties also will benefit from the new capabilities of ALMA,” the website added, such as the ability to “map gas and dust in the Milky Way and other galaxies, investigate ordinary stars, analyze gas from an erupting volcano on Jupiter’s moon, Io [and] study the origin of the solar wind.”
The first image from ALMA was a combined view of the Antennae Galaxies, which are about 75 million light-years from Earth. Another early image pierced dust surrounding the Centaurus A galaxy to show its bright center. The telescope is also capable of producing three-dimensional visualizations of gas, such as the image above of NGC 253 (the Sculptor Galaxy) released in 2013.
One of ALMA’s most prominent finds was announced in 2014 from examining a famed supernova remnant — the leftovers of supernova 1987A — and uncovering dust spewing in the area.
“We have found a remarkably large dust mass concentrated in the central part of the ejecta from a relatively young and nearby supernova,” astronomer Remy Indebetouw, of NRAO and the University of Virginia, said in a statement. “This is the first time we’ve been able to really image where the dust has formed, which is important in understanding the evolution of galaxies.”
A baby star was captured on camera in 2013 showing the youngster blasting out starstuff at 84,477 mph (144,000 kph). Once the material crashed into the surrounding gas, it produced a glow. This could provide some clues as to how the sun came together, astronomers said at the time. “The sun is a star, so if we want to understand how our solar system was created, we need to understand how stars are formed,” Héctor Arce, the lead author of the Astrophysical Journal study, said in a statement.
The formation of stars determines where new planetary systems can arise as well as the structure and evolution of galaxies. Learning more about star formation could help scientists understand the remaining mysteries about the birth of galaxies, including how the supermassive black holes at their hearts apparently originated so early in the universe’s history.
A dearth of data on the way matter is distributed within star-forming clouds has limited the accuracy of star formation models. Now scientists have developed a way to determine these details by using so-called dust-extinction maps, or observations of how dust scatters and absorbs light.
The birth of stars
Stars are born when pockets of gas and dust within interstellar molecular clouds exceed critical density and collapse under their own gravity. Once the pressure and the temperature inside get high enough for nuclear fusion to ignite, it creates a star. The rate at which stars form depends mainly on the number and density of these clumps within stellar nurseries.
Scientists have now used one feature of these clouds to better understand star formation. As the light of distant stars penetrates through a stellar nursery, the molecular cloud’s dust dims the light. By measuring how this process dims thousands of different stars, scientists can reconstruct the cloud’s 3D structure, helping pinpoint how matter is distributed within the cloud.
Using data from 16 nearby molecular clouds, each within about 850 light-years of Earth, “we could devise a very concrete recipe for how new stars are born in the interstellar gas clouds,” study lead author Jouni Kainulainen, an astrophysicist at the Max Planck Institute for Astronomy in Heidelberg, Germany, told Space.com. “And the ingredients of this recipe are simple to understand — only those regions in the clouds in which density is higher than about 5,000 molecules per cubic centimeter produce stars, and about a tenth of the gas in these regions collapses into the new stars.”
A clue for cosmic clouds
One key consequence of these findings “is that we have given astronomers a new tool to estimate the rates at which molecular clouds form stars, without even seeing the new stars in the clouds,” Kainulainen said. “I quote my collaborator Thomas Henning — ‘Show us your image of a cloud, and we can tell you how much it forms stars right now.’”
Such a capability “gives us a great possibility to use new, powerful telescopes such as the Atacama Large Millimeter/submillimeter Array (ALMA) to observe gas clouds in the galaxy and better map its star-formation capacity,” Kainulainen said. ALMA consists of 66 high-precision microwave antennas spread over distances of up to 10 miles (16 kilometers) in the Chilean desert, which can act like a single, high-resolution telescope. The array has just commenced operations.
Intriguingly, the researchers found it was simpler for stars to form in these clouds than once predicted by theory. But the findings have yet to address the question of how galaxies and supermassive black holes formed in the early universe, Kainulainen said. “I think it is currently too early to speculate about the possible effects of our findings to the early universe,” he said.
“We have to remember that physical conditions during the early galaxy formation were quite different from those of the galaxies today,” Kainulainen said. “It would be an unreasonable leap in conclusions to assume that the process of star formation would proceed exactly in the same way as in the current, local universe. Our results are best applicable to spiral galaxies such as the Milky Way in the local universe.”
Future studies should address the assumptions made in creating the team’s 3D models for the molecular clouds, Kainulainen said. “It is a good topic for future discussions — how this 3D modeling could potentially be improved,” he said. “I hope we will have comments and ideas from other scientists regarding this.”
Future research could determine what processes are most responsible for shaping molecular clouds.
“We know today very well that processes such as gravitational forces and magneto-hydrodynamic turbulence have a key role in shaping the clouds,” Kainulainen said. “With the parameters we have derived, we can answer questions such as, ‘In which regions is the cloud structure most crucially affected by turbulence, and in which by gravity?’ Such questions are of great importance in understanding the origin of interstellar gas clouds in galaxies and their evolution.”
Galaxies — those vast collections of stars that populate our universe — are all over the place. Perhaps the most resonant example of this fact is the Hubble eXtreme Deep Field, a collection of photographs from the Hubble Space Telescope revealing thousands of galaxies in a single composite picture.
Estimating how many galaxies are throughout the universe is a tougher job, however. Sheer numbers is one problem — once the count gets into the billions, it takes a while to do the addition. Another problem is the limitation of our instruments. To get the best view, a telescope needs to have a large aperture (the diameter of the main mirror or lens) and be located above the atmosphere to avoid distortion from Earth’s air.
While estimates among different experts vary, an acceptable range is between 100 billion and 200 billion galaxies, Mario Livio, an astrophysicist at the Space Telescope Science Institute in Baltimore, told Space.com.
To the best of Livio’s knowledge, Hubble is the best instrument available for galaxy counting and estimation. The telescope, launched in 1990, initially had a distortion on its main mirror that was corrected during a shuttle visit in 1993. Hubble also went underwent several upgrades and service visits until the final shuttle mission there in May 2009.
In 1995, astronomers pointed the telescope at what appeared to be an empty region of Ursa Major, and collected 10 days’ worth of observations. The result was an estimated 3,000 faint galaxies in a single frame, going as dim as 30th magnitude. (For comparison, the North Star or Polaris is at about 2nd magnitude.) This image composite was called the Hubble Deep Field and was the furthest anyone had seen into the universe at the time. [Related: Brightest Stars: Luminosity & Magnitude]
As the Hubble telescope received upgrades to its instruments, astronomers repeated the experiment twice. In 2003 and 2004, scientists created the Hubble Ultra Deep Field, which in a million-second exposure revealed about 10,000 galaxies in a small spot in the constellation Fornax.
In 2012, again using upgraded instruments, scientists used the telescope to look at a portion of the Ultra Deep Field. Even in this narrower field of view, astronomers were able to detect about 5,500 galaxies. Researchers dubbed this the eXtreme Deep Field.
All in all, Hubble reveals an estimated 100 billion galaxies in the universe or so, but this number is likely to increase to about 200 billion as telescope technology in space improves, Livio said.
Whatever instrument is used, the method of estimating the number of galaxies is the same. You take the portion of sky imaged by the telescope (in this case, Hubble). Then — using the ratio of the sliver of sky to the entire universe — you can determine the number of galaxies in the universe.
“This is assuming that there is no large cosmic variance, that the universe is homogenous,” Livio said. “We have good reasons to suspect that is the case. That is the cosmological principle.”
The principle dates back to Albert Einstein’s theory of general relativity at the turn of the last century. One of general relativity’s findings is that gravity is a distortion of space and time. With that understanding in hand, several scientists (including Einstein) tried to understand how gravity affected the entire universe.
“The simplest assumption to make is that if you viewed the contents of the universe with sufficiently poor vision, it would appear roughly the same everywhere and in every direction,” NASA stated. “That is, the matter in the universe is homogeneous and isotropic when averaged over very large scales. This is called the cosmological principle.”
One example of the cosmological principle at work is the cosmic microwave background, radiation that is a remnant of the early stages of the universe after the Big Bang. Using instruments such as NASA’s Wilkinson Microwave Anisotropy Probe, astronomers have found the CMB is virtually identical wherever one looks.
Would the number of galaxies change with time?
Measurements of the universe’s expansion — through watching galaxies race away from us — show that it is about 13.82 billion years old. As the universe gets older and bigger, however, galaxies will recede farther and farther from Earth. This will make them more difficult to see in telescopes.
The universe is expanding faster than the speed of light (which does not violate Einstein’s speed limit because the expansion is of the universe itself, rather than of objects traveling through the universe). Also, the universe is accelerating in its expansion.
This is where the concept of the “observable universe” — the universe that we can see — comes into play. In 1 trillion to 2 trillion years, Livio said, this means that there will be galaxies that are beyond what we can see from Earth.
“We can only see light from galaxies whose light had enough time to reach us,” Livio said. “It doesn’t mean that that’s all there is in the universe. Hence, the definition of the observable universe.”
Galaxies also change over time. The Milky Way is on a collision course with the nearby Andromeda Galaxy, and both will merge in about 4 billion years. Later on, other galaxies in our Local Group — the galaxies closest to us — will eventually combine. Residents of that future galaxy would have a much darker universe to observe, Livio said.
“Civilizations started then, they would have no evidence that there was a universe with 100 billion galaxies,” he said. “They would not see the expansion. They would probably not be able to tell there was a Big Bang.”
What about other universes?
As the early universe inflated, there are some theories that say that different “pockets” broke away and formed different universes. These different places could be expanding at different rates, include other types of matter, and have different physical laws than our own universe.
Livio pointed out there could be galaxies in these other universes — if they exist — but we have no way right now of knowing for sure. So the number of galaxies could even be greater than 200 billion, when considering other universes.
In our own cosmos, Livio said, astronomers will be better able to refine the number upon the launch of the James Webb Space Telescope (for which his institute will manage the mission operations and science). Hubble is able to peer back at galaxies that formed about 450 million years after the Big Bang. After James Webb launches in 2018, astronomers anticipate they can look as far back as 200 million years after the Big Bang.
“The numbers are not going to change much,” Livio added, pointing out the first galaxies probably formed not too long before that. “So a number like 200 billion [galaxies] is probably it for our observable universe.”