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The Expanding Universe: How the Universe Got Bigger As We Measured It

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Since before history began, we have tried to understand our world and our place in it. To the earliest hunter-gatherer tribes, this meant little more than knowing the tribe's territory. But as people began to settle and trade, knowing the wider world became more important, and people became interested in the actual size of it. Aristarchus of Samos (310-230 BC) made the earliest surviving measurements of the distance between objects in space. By carefully measuring the apparent size of the Sun and Moon and carefully observing the terminator of the Moon when half full, he concluded that the Sun was 18-20 times farther away than the Moon. The actual value is 400, but he was on the right track; he just didn't have precise enough measurements.


A diagram from Aristarchus' work, "On Size and Distances," describing how to work out the relative distances.

Meanwhile, Eratosthenes of Cyrene (276-195 BC) was working on the size of the Earth. He came upon a letter stating that at noon in Syene (modern-day Aswan) on the summer solstice, one could look down a well and see all the way to the bottom because the Sun was precisely overhead. Eratosthenes already knew the distance between Alexandria and Syene, so all he had to do was observe the angle of the Sun on the summer solstice there and then do a little math. Assuming a spherical Earth, he computed the circumference to be 252,000 stadia, which works out to 39,690 km -- which is less than a 2% error compared to the real value. A directly measured size now existed for the world. But what of the heavens? The work of Aristarchus wasn't accurate enough. After figuring out how to reliably predict eclipses, Hipparchus (190-120 BC) used them to get a better estimate of the ratio of distance between Moon and Sun. He concluded that the Moon was 60.5 Earth radii away, and the Sun was 2,550 Earth radii away. His lunar distance was pretty accurate -- that works out to 385,445 km to the Moon, which is pretty close to the actual distance, an average of 384,400 km -- but for the Sun it worked out to 16 million km, about 136 million km short of the actual distance.

Above left: A dioptra, a predecessor to both the astrolabe and the theodolite, of a type similar to the one Hipparchus used to make his measurements.

When Ptolemy (AD 90-168) came along, the Universe shrank for a while.

Using the epicycles he assumed must exist within his geocentric universe, he estimated the distance to the Sun to be 1,210 Earth radii, and the distance to the fixed stars to be 20,000 Earth radii away; using modern values for the Earth's average radius, that gives us 7,708,910 km to the Sun and 127,420,000 km to the fixed stars. Both of those are woefully small (Ptolemy's universe would fit within the orbit of Earth), but they get even smaller if we use his smaller estimate for the Earth's circumference -- he estimated the Earth to be about 1/6 the size it actually is. (And therein hangs a tale, for Christopher Columbus would try to use Ptolemy's figure when plotting his journey west to the Orient, rather than the more accurate ones that had been developed in Persia since then.)


Ptolemy's world; at the time, the best map that existed of the known world.

By the end of the 16th Century, the size of the Earth was pretty well defined, but the size of the Universe remained challenging. Johannes Kepler solved the puzzle of orbital motion and calculated the ratio of the distance between Sun and various planets, enabling accurate predictions of transits. In 1639, Jeremiah Horrocks made the first known observation of a transit of Venus. He estimated the distance between Earth and the Sun at 95.6 million km, the most accurate estimate to date (and about 2/3 the actual distance). In 1676, Edmund Halley attempted to measure solar parallax during a transit of Mercury, but was unsatisfied with the only other observation made. He proposed that further observations be made during the next transit of Venus, in 1761. Unfortunately, he did not live that long.



Jeremiah Horrocks, observing the transit of Venus by the telescopic projection method.

In 1761, acting on the recommendations of the late Edmund Halley, scientific expeditions set out to observe the Transit of Venus from as many places as possible. More expeditions set out in 1769 for the second transit of the pair, including a famous journey by Captain James Cook to Tahiti, and in 1771, Jerome Lalande used the data to calculate the Sun's average distance as 153 million km, far larger than previously estimated, and the first time the measurement was close to right. Further transits in 1874 and 1882 refined the distance to 149.59 million km. In the 20th Century, it has been refined further using radio telemetry and radar observations of the inner planets, but it has not strayed much from that value. The size of the solar system was now known.

Above left: Sketch depicting the transit circumstances, as reported by James Ferguson, a Scottish self-taught scientist and inventor who participated in the transit observations.

But the universe is bigger than the solar system. In the 1780s, William Herschel mapped the visible stars in an effort to find binary stars. He found quite a few, but he also worked out that the solar system was actually moving through space, and that the Milky Way was disk shaped. The galaxy, which was at that time synonymous with Universe, was eventually estimated to be about 30,000 light years across -- an inconceivably large distance, but still far too small.

Hershel's map of the galaxy could not tell how far away any of the stars were; stars get dimmer as they move away, but you can only use this to calculate their distance if you know how bright they are to begin with, and how can you know that? In 1908, Henrietta Leavitt found the answer: she noticed that Cepheid variable stars had a direct relationship between their luminosity and the period of their variation, allowing astronomers to deduce exactly how bright they are to start with. Harlow Shapley immediately applied this discovery and found three amazing things when he mapped all the visible Cepheids: the Sun is actually nowhere near the center of the galaxy, the center of the galaxy is obscured by vast amounts of dust, and the galaxy is at least ten times larger than anyone had ever suspected -- so vast that it would take light 300,000 years to cross it. (Shapley was overestimating a bit; it's actually more like 100,000 light years or so.)

Above left: Henrietta Leavitt, one of the few women in astronomy and the only one on this list; she got little recognition for her discovery at the time.

In 1924, Edwin Hubble produced the next major revolution. Using the new 100-inch telescope at Mount Wilson Observatory, he located Cepheids in the Andromeda Nebula, a spiral nebula in which no stars had previously been resolved. He calculated these Cepheids were 1.2 million light years away, putting them far beyond Shapley's wildest estimate for the size of the galaxy. Therefore, Andromeda was not a part of our galaxy at all; it was an entirely separate "island universe," and most likely the same was true of other spiral nebulae. This meant the Universe was very likely far larger than anyone could hope to measure. It could even be infinite.

At left: The 100-inch telescope at Mount Wilson Observatory, where Hubble did his work. It was the world's largest telescope until 1948.

And then Hubble found something even more astonishing. In 1929, Hubble compared the spectra of near and far galaxies, based on distances already known by observations of Cepheid variables. The spectra of more distant ones were consistently redder, and for nearly all of them, there was a linear relationship between redshift and distance. Due to the Doppler Effect, this meant they were receding. He wasn't sure what to make of this observation at the time, but in 1930, Georges Lemaître pointed out a possible solution: he suggested that the universe was expanding, carrying galaxies along with it, and that at one time it had all be compacted down impossibly tight. Hubble went with this and calibrated the apparent expansion against the distance to known standard candles, calculating the age of the most distant objects to be 1.8 billion light years.

At left: Georges Lemaître, who happened to also be a Catholic priest. He died in 1966, shortly after learning about the Cosmic Microwave Background radiation, which further reinforced his theory of the Big Bang.

This was much too small, and in 1952, Walter Baade figured out why: there are actually two kinds of Cepheids, and Hubble had been observing the ones that Leavitt had not baselined. After characterizing this new population of Cepheids, he recalculated from Hubble's observations and brought the Universe's minimum age up to 3.6 billion years. In 1958, Allan Sandage improved it more, to an estimated 5.5 billion years.

Astronomers started to ratchet up their observations of ever more distant objects. In 1998, studies of very distant Type 1A supernovae revealed a new surprise: not only is the universe expanding, but the rate of the expansion is increasing. Today, the Universe is usually estimated to be 13.7 billion years old -- or, more accurately, the most distant things we can observe appear to be that far away. The catch, of course, is that we're observing them in the past. They're actually further away now -- assuming, of course, that they even still exist. A lot can happen in 13.75 billion years. And now that we know the universe's expansion is accelerating, they are even farther away by now. The current estimate for the actual size of the observable universe is 93 billion light-years in diameter, a tremendous size that the human brain cannot begin to fathom on its own, vastly overwhelming the tiny universe of the ancient Greeks.


NASA artist's concept of the progenitor of a Type 1a supernova -- a neutron star stealing matter from a supergiant companion until eventually enough matter is collected to trigger a supernova.

The understanding of the size of the Universe has gone from being impressed by the distance to the Sun, to the size of the solar system, to the vastness of the galaxy, to the staggering distance to neighboring galaxies, to the mindbendingly complicated distances to things that we can only see as they were an impossibly long period of time ago. What will we discover as we measure the Universe tomorrow?

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NSF/LIGO/Sonoma State University/A. Simonnet
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Space
Astronomers Observe a New Kind of Massive Cosmic Collision for the First Time
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NSF/LIGO/Sonoma State University/A. Simonnet

For the first time, astronomers have detected the colossal blast produced by the merger of two neutron stars—and they've recorded it both via the gravitational waves the event produced, as well as the flash of light it emitted.

Physicists believe that the pair of neutron stars—ultra-dense stars formed when a massive star collapses, following a supernova explosion—had been locked in a death spiral just before their final collision and merger. As they spiraled inward, a burst of gravitational waves was released; when they finally smashed together, high-energy electromagnetic radiation known as gamma rays were emitted. In the days that followed, electromagnetic radiation at many other wavelengths—X-rays, ultraviolet, optical, infrared, and radio waves—were released. (Imagine all the instruments in an orchestra, from the lowest bassoons to the highest piccolos, playing a short, loud note all at once.)

This is the first time such a collision has been observed, as well as the first time that both kinds of observations—gravitational waves and electromagnetic radiation—have been recorded from the same event, a feat that required co-operation among some 70 different observatories around the world, including ground-based observatories, orbiting telescopes, the U.S. LIGO (Laser Interferometer Gravitational-Wave Observatory), and European Virgo gravitational wave detectors.

"For me, it feels like the dawning of a next era in astrophysics," Julie McEnery, project scientist for NASA's Fermi Gamma-ray Space Telescope, one of the first instruments to record the burst of energy from the cosmic collision, tells Mental Floss. "With this observation, we've connected these new gravitational wave observations to the rest of the observations that we've been doing in astrophysics for a very long time."

A BREAKTHROUGH ON SEVERAL FRONTS

The observations represent a breakthrough on several fronts. Until now, the only events detected via gravitational waves have been mergers of black holes; with these new results, it seems likely that gravitational wave technology—which is still in its infancy—will open many new phenomena to scientific scrutiny. At the same time, very little was known about the physics of neutron stars—especially their violent, final moments—until now. The observations are also shedding new light on the origin of gamma-ray bursts (GRBs)—extremely energetic explosions seen in distant galaxies. As well, the research may offer clues as to how the heavier elements, such as gold, platinum, and uranium, formed.

Astronomers around the world are thrilled by the latest findings, as today's flurry of excitement attests. The LIGO-Virgo results are being published today in the journal Physical Review Letters; further articles are due to be published in other journals, including Nature and Science, in the weeks ahead. Scientists also described the findings today at press briefings hosted by the National Science Foundation (the agency that funds LIGO) in Washington, and at the headquarters of the European Southern Observatory in Garching, Germany.

(Rumors of the breakthrough had been swirling for weeks; in August, astronomer J. Craig Wheeler of the University of Texas at Austin tweeted, "New LIGO. Source with optical counterpart. Blow your sox off!" He and another scientist who tweeted have since apologized for doing so prematurely, but this morning, minutes after the news officially broke, Wheeler tweeted, "Socks off!") 

The neutron star merger happened in a galaxy known as NGC 4993, located some 130 million light years from our own Milky Way, in the direction of the southern constellation Hydra.

Gravitational wave astronomy is barely a year and a half old. The first detection of gravitational waves—physicists describe them as ripples in space-time—came in fall 2015, when the signal from a pair of merging black holes was recorded by the LIGO detectors. The discovery was announced in February 2016 to great fanfare, and was honored with this year's Nobel Prize in Physics. Virgo, a European gravitational wave detector, went online in 2007 and was upgraded last year; together, they allow astronomers to accurately pin down the location of gravitational wave sources for the first time. The addition of Virgo also allows for a greater sensitivity than LIGO could achieve on its own.

LIGO previously recorded four different instances of colliding black holes—objects with masses between seven times the mass of the Sun and a bit less than 40 times the mass of the Sun. This new signal was weaker than that produced by the black holes, but also lasted longer, persisting for about 100 seconds; the data suggested the objects were too small to be black holes, but instead were neutron stars, with masses of about 1.1 and 1.6 times the Sun's mass. (In spite of their heft, neutron stars are tiny, with diameters of only a dozen or so miles.) Another key difference is that while black hole collisions can be detected only via gravitational waves—black holes are black, after all—neutron star collisions can actually be seen.

"EXACTLY WHAT WE'D HOPE TO SEE"

When the gravitational wave signal was recorded, on the morning of August 17, observatories around the world were notified and began scanning the sky in search of an optical counterpart. Even before the LIGO bulletin went out, however, the orbiting Fermi telescope, which can receive high-energy gamma rays from all directions in the sky at once, had caught something, receiving a signal less than two seconds after the gravitational wave signal tripped the LIGO detectors. This was presumed to be a gamma-ray burst, an explosion of gamma rays seen in deep space. Astronomers had recorded such bursts sporadically since the 1960s; however, their physical cause was never certain. Merging neutron stars had been a suggested culprit for at least some of these explosions.

"This is exactly what we'd hoped to see," says McEnery. "A gamma ray burst requires a colossal release of energy, and one of the hypotheses for what powers at least some of them—the ones that have durations of less than two seconds—was the merger of two neutron stars … We had hoped that we would see a gamma ray burst and a gravitational wave signal together, so it's fantastic to finally actually do this."

With preliminary data from LIGO and Virgo, combined with the Fermi data, scientists could tell with reasonable precision what direction in the sky the signal had come from—and dozens of telescopes at observatories around the world, including the U.S. Gemini telescopes, the European Very Large Telescope, and the Hubble Space Telescope, were quickly re-aimed toward Hydra, in the direction of reported signal.

The telescopes at the Las Campanas Observatory in Chile were well-placed for getting a first look—because the bulletin arrived in the morning, however, they had to wait until the sun dropped below the horizon.

"We had about eight to 10 hours, until sunset in Chile, to prepare for this," Maria Drout, an astronomer at the Carnegie Observatories in in Pasadena, California, which runs the Las Campanas telescopes, tells Mental Floss. She was connected by Skype to the astronomers in the control rooms of three different telescopes at Las Campanas, as they prepared to train their telescopes at the target region. "Usually you prepare a month in advance for an observing run on these telescopes, but this was all happening in a few hours," Drout says. She and her colleagues prepared a target list of about 100 galaxies, but less than one-tenth of the way through the list, by luck, they found it: a tiny blip of light in NGC 4993 that wasn't visible on archival images of the same galaxy. (It was the 1-meter Swope telescope that snagged the first images.)

A NEW ERA OF ASTROPHYSICS

When a new star-like object in a distant galaxy is spotted, a typical first guess is that it's a supernova (an exploding star). But this new object was changing very rapidly, growing 100 times dimmer over just a few days while also quickly becoming redder—which supernovae don't do, explains Drout, who is cross-appointed at the Dunlap Institute for Astronomy and Astrophysics at the University of Toronto. "We ended up following it for three weeks or so, and by the end, it was very clear that this [neutron star merger] was what we were looking at," she says.

The researchers say they can't be sure if the resulting object was another, larger neutron star, or whether it would have been so massive that it would have collapsed into a black hole.

As exciting as the original detection of gravitational waves last year was, Drout is looking forward to a new era in which both gravitational waves and traditional telescopes can be used to study the same objects. "We can learn a lot more about these types of extreme systems that exist in the universe, by coupling the two together," she says.

The detection shows that "gravitational wave science is moving from being a physics experiment to being a tool for astronomers," Marcia Rieke, an astronomer at the University of Arizona who is not involved in the current research, tells Mental Floss. "So I think it's a pretty big deal."

Physicists are also learning something new about the origin of the heaviest elements in the periodic table. For many years, these were thought to arise from supernova explosions, but spectroscopic data from the newly observed neutron star merger (in which light is broken up into its component colors) suggests that such explosion produce enormous quantities of heavy elements—including enough gold to put Fort Knox to shame. (The blast is believed to have created some 200 Earth-masses of gold, the scientists say.) "It's telling us that most of the gold that we know about is produced in these mergers, and not in supernovae," McEnery says.

Editor's note: This post has been updated.

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Space
Send Your Name to Space on NASA's Latest Mars Lander
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NASA/JPL-Caltech

Humans may not reach Mars until the 2030s (optimistically), but you can get your name there a whole lot sooner. As Space.com reports, NASA is accepting names from the public to be engraved on a small silicon microchip that's being sent into space with their latest Mars lander, InSight.

All you have to do is submit your name online to NASA, and the space agency will put it on the lander—in super-tiny form, of course—which will set off for Mars in May 2018.

This is the public's second shot at getting their name to Mars: NASA first put out a call for names to go to the Red Planet with InSight in 2015. The planned 2016 launch was delayed over an issue with one of the instruments, and since the naming initiative was so popular—almost 827,000 people submitted their names the first time around—they decided to open the opportunity back up and add a second microchip.

A scientist positions the microchip on the InSight lander.
NASA/JPL-Caltech/Lockheed Martin

NASA is encouraging people to sign up even if they've sent in their names for other mission microchips. (The space agency also sent 1.38 million names up with Orion's first test flight in 2014.) You can put your name on both of InSight's microchips, in other words, as well as any future missions. The agency's "frequent flyer" program allows you to keep track of every mission to which your name is attached. Interplanetary fame, here you come.

You can submit your name for the InSight mission until November 1 using this form. If you miss the deadline, though, don't worry too much: You'll soon be able to submit your name for Exploration Mission-1's November 2018 launch.

[h/t Space.com]

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