Using the Hubble Space telescope and other observatories, astronomers have completed the most accurate census of galaxies in the observable universe to date. In terms of the actual number, let’s just say we were way the hell off.
The observable universe—that is, the part of the universe that’s visible to us on Earth—contains 10 to 20 times as many galaxies than previous estimates. That raises the total to somewhere between one and two trillion galaxies, which is up from the previous best estimate of 100 billion galaxies. Consequently, this means we also have to update the number of stars in the observable universe, which now numbers around 700 sextillion (that’s a 7 with 23 zeros behind it, or 700 thousand billion billion).
And that’s just within the observable universe. Because the cosmos emerged some 13.8 billion years ago, we’re only able to observe objects up to a certain distance from Earth. Anything outside this “Hubble Bubble” is invisible to us because the light from these distant objects simply haven’t had enough time to reach us. It’s difficult—if not impossible—to know how many galaxies reside outside this cosmological blind spot.
To come up with the new figure, an international team of astronomers led by Christopher Conselice from the University of Nottingham, UK, used deep space images from Hubble, and combined them with data collected by other astronomers. The images were converted into 3D, allowing the researchers to make accurate measurements of the number of galaxies at various stages in the universe’s history.
They were able to peer back into time, showing that the early universe was cluttered with many tiny galaxies, which eventually merged with other tiny galaxies, forming many of the larger objects we see today. The results of this latest celestial survey, which are set to be published in the Astrophysical Journal, shows the significant degree to which galaxies have evolved over the course of the universe’s history.
Using new mathematical models, the astronomers were also able to infer the existence of galaxies that the current generation of telescopes cannot detect. The researchers say there must be a further 90 percent of galaxies in the observable universe that are too dim and far away for us to see using current telescopes.
“It boggles the mind that over 90 percent of the galaxies in the universe have yet to be studied,” noted Conselice. “Who knows what interesting properties we will find when we discover these galaxies with future generations of telescopes?”
Astronomers at the University of Minnesota Duluth and the North Carolina Museum of Natural Sciences have identified a new class of ring galaxy. Named PGC 1000714, it features an elliptical core with not one, but two outer rings. It’s the only known galaxy of its kind in the known universe.
Most galaxies are either disc-shaped spirals or egg-shaped ellipticals, but there are some oddballs as well, such as lenticular galaxies (kind of a cross between spirals and ellipticals), irregular galaxies (which don’t really have a discernable shape or structure), and extremely-low density galaxies known as ultra diffuse objects.
Among these oddballs are ring galaxies—beautiful celestial objects featuring a well-defined elliptical core that’s surrounded by a single ring of stars—and with nothing visibly connecting them. The most famous of these is Hoag’s Object(pictured at left), which was discovered in 1950, and is named in honor of the astronomer who first spotted it, Arthur Hoag. Ring galaxies, also known as Hoag-objects, are exceptionally rare in the universe—less than 0.1 percent of all observed galaxies are Hoag-type galaxies—and astronomers make a big fuss whenever one is discovered.
According to a new study published in the Monthly Notices of the Royal Astronomical Society, we can add a new ring galaxy to this very short list—but it’s a ring galaxy that deserves a sub-classification of its own: an elliptical core surrounded by two discernable and independent rings.
The object, known as PGC 1000714, or Burcin’s Galaxy (named after the lead author of the paper, Burcin Mutlu-Pakdil), is located approximately 359 million light-years away, and its unusual structure is providing astronomers with unique insights into how galaxies form and evolve.
By analyzing multi-waveband images of the galaxy, the researchers detected a blue, i.e. young, outer ring (about 0.13 billion years old), surrounded by a red, i.e. older, central elliptical core (about 5.5 billion years old). Unexpectedly, they also discovered a second inner ring around the central body.
“We’ve observed galaxies with a blue ring around a central red body before, the most well-known of these is Hoag’s object. However, the unique feature of this galaxy is what appears to be an older diffuse red inner ring,” noted Patrick Treuthardt, co-author of the study and an astrophysicist at the North Carolina Museum of Natural Sciences, in a statement.
Astronomers aren’t entirely sure how ring galaxies form, but it’s possible that their outer regions emerge as the result of colliding gas. “The different colors of the inner and outer ring suggest that this galaxy has experienced two different formation periods,” said Mutlu-Pakdil. That said, the researchers believe it’s practically impossible to know how the rings of this particular galaxy formed.
“Whenever we find a unique or strange object to study, it challenges our current theories and assumptions about how the universe works,” said Treuthardt. “It usually tells us that we still have a lot to learn.”
A long time ago in two galaxies far, far away, there was quite the kerfuffle. New research suggests that about 200 million years ago, the Large Magellanic Cloud, a satellite galaxy of the Milky Way located 160,000 lightyears from Earth, got into an intergalactic altercation with its younger sibling, the Small Magellanic Cloud. But the best part is what came after.
Christian Moni Bidin and his team of researchers at the Catholic University of the North in Antofagasta, Chile are studying one possible aftermath of the scuffle. The group believes a ring of six young stars it found at the edge of the Large Magellanic Cloud, similar to the bright blue stars pictured above, were probably born after the the Small Magellanic Cloud smashed into it. Galaxy collisions happen when gravity pulls the two star-filled masses toward each other. Bidin and his team believe that in this case, after the galaxies collided, their gas and dust compressed, giving birth to the six new stars. The team’s work has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.
Oddly enough, five of the six stars are located among much older stars. Though the stars are notably younger than the possible collision that created them—between 10 and 50 million years old—Bidin says this doesn’t disprove the group’s findings.
“It was surprising,” Bidin told New Scientist. “There was no indication of recent star formation in this region.”
The team says it will be eagerly pursuing more stars that could have come out of the intergalactic rumpus.
“We studied the tip of the iceberg,” he said. “There could be many fainter stars.”
Welcome back to Giz Asks, a series where we ask experts hard questions about science, technology, and humanity’s future. Today, we’re wondering about the “speed of dark,” and for that matter, the scientific nature of “speed” and “darkness.”
The speed of light is one of the most important constants in physics. First measured by Danish astronomer Olaus Roemer in 1676, it was Albert Einstein who realized that light sets an ultimate speed limit for our universe, of 186,000 rip-roaring miles per second. But while the immutability of lightspeed is drilled into physics students at a young age, Einstein’s laws also state that all motion is relative, which got us thinking: what’s the speed of light’s nefarious doppleganger, darkness?
We’re not the first to ask this question (shout out comedian Steven Wright) or take it seriously, but in asking scientists and researchers, we left the interpretation of “darkness” open, eliciting some fascinating responses from experts on black holes and quantum physics. It turns out, darkness could be just as fast as light, or it could be infinitely slower—it all depends on your perspective.
The speed of dark? The easy answer is that it’s just the speed of light. Switch off the sun and our sky would go dark eight minutes later. But easy is boring! For starters, what we commonly call the “speed of light” is the speed of propagation, and that’s not always the deciding factor. A shadow swoops across the landscape at a speed governed by the object that casts it. For instance, as a lighthouse beacon rotates, it lights up the surroundings at regular intervals. The ground speed of its shadow increases with distance from the lighthouse.
While we’re at it, is there even such a thing as darkness? If you did switch off the sun, Earth wouldn’t go completely dark. Light from stars, nebulae, and the big bang would fill the sky. The planet and everything on it, including our bodies, would blaze in the infrared. Depending on how, exactly, you’d managed to switch the sun off, it would keep on glowing for eons. As long as we were able to see, we’d see something. No light detector can register total darkness, because, if nothing else, quantum fluctuations produce tiny flashes of light. Even a black hole, the darkest conceivable object, emits some light. In physics, unlike human affairs, light always chases away dark.
Darkness isn’t a physical category, but a state of mind. Photons hitting, or not hitting, retinal cells may trigger the experience, but do not explain the subjective experience of darkness, any more than the length of waves explains the experience of color or sound. Our conscious experience changes from moment to moment, but the individual frames of that experience are timeless. In that sense, darkness has no speed.
And what about speed in general—is there such a thing? It presupposes a framework of space, and scientists see phenomena in quantum physics where spatial concepts seem not to apply—suggesting, to some, that space is derived from a more fundamental level of reality where these is no such as thing as position, distance, or speed. It must be the level that Steven Wright operates on.
Close to a black hole, matter falls in at a speed that is close to the speed of light. Once it enters the so-called event-horizon of the black holes, nothing can escape. Even light is trapped inside the horizon forever. Hence a black hole can be thought of as the ultimate prison.
A star like the Sun can be shredded (“spaghettified”) into a stream of gas if it passes too close to a massive black hole, like the one (weighting six billion solar masses) at the center of the Milky Way galaxy.
As matter falls into the black hole, it often rubs against itself and heats up. As a result it radiates. If the accretion rate is high enough, the force of the radiation flowing out could potentially stop additional matter from falling in. Many of the most massive black holes in the universe, weighting billions of solar masses, are observed to accrete at the maximum possible rate (also called the Eddington limit, after Sir Arthur Eddington who discovered theoretically the maximum radiation output possible for gravity to overcome the radiation force).
Neil DeGrasse Tyson
Director of the Hayden Planetarium at the Rose Center for Earth and Space, research associate and founder of the Department of Astrophysics at the American Museum of Natural History, host of Cosmos: A Spacetime Odyssey
The speed of dark… Consider dark getting erased by light. The light erases it at the speed of light so the speed of dark would be negative the speed of light. If light is a vector, it has magnitude and direction, so… to call it negative means it’s in a negative direction. The dark is receding rather than advancing. I’d call it negative the speed of light.
Postdoctoral Researcher at Leonard E. Parker Center for Gravitation, Cosmology & Astrophysics, University of Wisconsin-Milwaukee
A black hole has gravity so strong that not even light can escape once it has passed the event horizon, an invisible boundary marking the point of no return. Because the black hole has such strong gravity, time dilation will affect observations from outside the strong gravitational field.
For example, a distant observer watching a glowing object fall into a black hole will see it slow down and fade, eventually becoming so dim it cannot be seen. This observer won’t ever see the object cross the event horizon.
We can also take the perspective of stuff falling into the black hole, instead of a distant observer. For example, if we take a black hole in the center of a glowing gas cloud, say from a star that has been broken up by passing too close to the black hole, the material will form a flattened disk, known as an accretion disk. This gas will fall into the black hole, but it is not instantaneous. There is a speed limit enforced by the radiation pressure from the hot gas which will fight against the inward force of gravity from the black hole. As the gas falls into the black hole, the black hole grows in size. If a black hole that is 10 times as massive as our Sun is accreting at the maximum allowed rate, in about a billion years it could have reached 100 million times the mass of our Sun.
Executive Director of LIGO Laboratory at the California Institute of Technology
Basically, it depends on whether you’re the matter being consumed by the infinite abyss of a black hole or you’re far enough away to be a dispassionate observer watching someone else falling into the infinite abyss. If you happen to be the unlucky matter falling in, the speed is potentially very large, in principle approaching the speed of light.
If you’re the observer and you’re far enough away, the speed with which matter is consumed is dramatically slowed down due to an effect known as gravitational time dilation—clocks run slower in gravitational fields, and much slower in the immense gravitational fields near the event horizon of the black hole. By ‘far enough away’, I mean that in your local reference frame, your stationary relative to the black hole (i.e, not getting sucked in) and your local clock is not affected by the gravitational field of the black hole. In fact, to the far away person it will take an infinite amount of time for something to travel to the event horizon of the black hole.
Associate Professor of Astrophysics and Gravitation in the Department of Physics and Astronomy at the University of Waterloo, Associate Faculty of Cosmology and Gravitation at the Perimeter Institute for Theoretical Physic (PI)
I believe the speed “of dark” is infinite! In classical physics, the vast darkness of space could be just empty vacuum. However, we have learnt from quantum mechanics that there is no real dark or empty space. Even where there is no light that we can see, electromagnetic field can fluctuate in and out of existence, especially on small scales and short times. Even gravitational waves, the ripples in the geometry of spacetime that were recently observed by the LIGO observatory, should have these quantum fluctuations.
The problem is that the gravity of these quantum ripples is infinite. In other words, currently there is no sensible theory of quantum gravity that people could agree on. One way to avoid the problem is if the speed “of dark”, i.e. the quantum ripples, goes to infinity (or becomes arbitrarily big) on small scales and short times. Of course, that’s only one possibility, but is a simple (and my favourite) way to understand big bang, black holes, dark energy, and quantum gravity.
This is not a truck. Adam Makarenko creates slightly paranormal stories using photographs of meticulously-crafted miniatures. Here you’re peeking at part of a tale that dreamily evokes a beehive’s life. First, the bees are stacked in their boxes on the back of a truck — transported to a new home. Later, they join the ecosystem in a place that’s full of bears. You can see a lot more of Makarenko’s work on his website.
This isn’t some neat CGI wallpaper or a bit of deep space photography. It’s a gorgeously detailed picture of a practical model, hand-made and then intricately shot to a make it look just as good as any scifi vista you’ll see in on screen.
As part of a new series, photographer Adam Makarenko uses his modelmaking know-how—which we’ve featured before on io9—to craft intricate fictional landscapes and exoplanets, before shooting them to look like they’re the latest stellar photography straight from a deep space mission. They’re simply presented, but the crazy work that goes into making these worlds look real is nothing short of remarkable.