Amazing astronomy: How neutron stars create ripples in space-time

What can cause a ripple in both space and time? Neutron stars colliding. And what can observe that phenomenon? A two-mile-long laser.

Michelle Thaller: A few decades ago we actually saw explosions in the sky somewhere out in space that we really didn’t understand at all. They gave intense bursts to something called gamma rays. And gamma rays are the highest energy kind of light that is possible. Now you probably heard of, you know, ultraviolet rays from the sun, they give you sunburn. And then there are things like x-rays. Gamma rays are even more energetic and more dangerous to us than that. But gamma rays are only created in the universe by things that are naturally in the billions of degrees. And we saw these little gamma ray pops going off in space. At first we wondered well are they nearby? Could they be in our own galaxy or are they very far away? We really didn’t know. And a few decades ago we actually realized that these gamma-ray bursts were coming from very, very distant galaxies. Galaxies that in most cases were billions of light-years away. A light-year is about six trillion miles, the distance that light travels in one year. So billions of light-years away. And so something was creating a lot of gamma rays because they were bright enough to measure from that distance. And incredibly some of these explosions were so intense – there was one I believe it was in 2007 that NASA observed. There was a little flash of visible light that came with the gamma rays and it was actually visible with the naked eye for a couple of minutes. If you were actually in the southern hemisphere on that night you would have seen a little star turn on and off for a couple of minutes and then it would have been gone.

And that explosion happened about seven billion light-years away. Something blew up seven billion years ago on almost the other side of the observable universe and it was bright enough to see with the unaided eye. We had discovered something unbelievable. What could possibly be that bright? What could possibly be that violent? That little explosion for a few minutes outshone the rest of the observable universe. Just one thing. So we really didn’t know what could possibly create that much energy. And the theoretical physicists got to work and they started just kind of guessing. I mean what could explode that could make that much energy? And it turns out that if you have these things called neutron stars. Neutron stars are the leftover compressed cores of dead stars. They are amazing monsters. They’re about ten miles across and they have a density that if you had about a teaspoonful of the material that that would be about as much as the mass as Mount Everest crushed into a teaspoonful. They’re amazing things and we observe hundreds, thousands of these things in space. And so people sort of theorize that if two of these things spiral together and collided you would actually be able to get that much energy out. It seemed unlikely but, you know, maybe that does happen sometime in the universe, the two of these things collide. Now Einstein came up with this wonderful idea that space and time is almost kind of like a fabric that connects everything in the universe. And what gravity is is gravity is kind of a pulling and a stretching on that fabric.

And if you have two really massive things moving around each other very fast before they collide. Say two neutron stars spiraling in. They should actually make ripples in this fabric. So as they spiral closer and closer together they actually make ripples that actually go out through space at the speed of light. And these are called gravitational waves. And they are very, very hard to find. I mean lucky for us masses moving around only create tiny little distortions in space and time. The fabric of space and time itself. So what happens is we actually started building instruments that were sensitive enough. Sensitive enough to detect this tiny little wobble in space and time itself. And to give you an idea about how hard this is to detect we used an instrument called LIGO, the Laser Interferometric Gravitational-Wave Observatory. And LIGO has two lasers and the lasers are about two miles long and they’re actually at a right angle. So two-mile long lasers at a sort of a corner shape. And the idea was that if one of these ripples in space and time comes through one of the sides of the laser in this corner construction would actually be warped a little more than the other and you’d actually see that space and time itself were changing a little more in one direction as this ripple came through. The ripple is so small that over a two-mile laser the distance space and time changes is by about a thousandth of a diameter of a proton. We have an instrument that can measure that and amazingly we started seeing these ripples coming from many different places in the sky as these neutron stars collided and spiraled together. And the thing that was so wonderful – this only happened last year – is that one of these gamma-ray bursts, one of these ultraviolet explosions that we have no idea really what they could be went off. And at the same time at the speed of light with those gamma rays came that ripple, that signal that exactly matched two neutron stars spiraling together. We had guessed that the only thing that could actually make that much energy were these two dead stars colliding and now we had evidence. And the evidence was a ripple in space and time a thousand times smaller than a proton.

Michell Thaller, the Assistant Director of Science Communication at NASA, wanted to talk to us about a heavy subject matter. Specifically, super-dense neutron stars that are so dense that they're only the size of New York City but carry the weight of the sun. And when they circle each other in orbit for long enough, they collide with enough force to send ripples in both space and time. Those ripples alone are strong enough to alter the course of light. In fact, just a few years ago a rare astronomical event occurred where you'd have seen a star "blink" for a few minutes on and off before disappearing for good. Scientists are able to detect these gravitational ripples thanks to a LIGO, or a Laser Interferometric Gravitational-Wave Observatory, which measures the refraction of light based on gravity waves. Oh, and one more thing: Albert Einstein correctly deduced that this phenomenon years before it was ever recorded. If you'd like to know more, visit NASA.

Participatory democracy is presumed to be the gold standard. Here’s why it isn’t.

Political activism may get people invested in politics, and affect urgently needed change, but it comes at the expense of tolerance and healthy democratic norms.

Photo by Nicholas Roberts /Getty Images
Sponsored by Charles Koch Foundation
  • Polarization and extreme partisanships have been on the rise in the United States.
  • Political psychologist Diana Mutz argues that we need more deliberation, not political activism, to keep our democracy robust.
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How do 80-year-old 'super-agers' have the brains of 20-somethings?

Most elderly individuals' brains degrade over time, but some match — or even outperform — younger individuals on cognitive tests.

Mind & Brain
  • "Super-agers" seem to escape the decline in cognitive function that affects most of the elderly population.
  • New research suggests this is because of higher functional connectivity in key brain networks.
  • It's not clear what the specific reason for this is, but research has uncovered several activities that encourage greater brain health in old age.

At some point in our 20s or 30s, something starts to change in our brains. They begin to shrink a little bit. The myelin that insulates our nerves begins to lose some of its integrity. Fewer and fewer chemical messages get sent as our brains make fewer neurotransmitters.

As we get older, these processes increase. Brain weight decreases by about 5 percent per decade after 40. The frontal lobe and hippocampus — areas related to memory encoding — begin to shrink mainly around 60 or 70. But this is just an unfortunate reality; you can't always be young, and things will begin to break down eventually. That's part of the reason why some individuals think that we should all hope for a life that ends by 75, before the worst effects of time sink in.

But this might be a touch premature. Some lucky individuals seem to resist these destructive forces working on our brains. In cognitive tests, these 80-year-old "super-agers" perform just as well as individuals in their 20s.

Just as sharp as the whippersnappers

To find out what's behind the phenomenon of super-agers, researchers conducted a study examining the brains and cognitive performances of two groups: 41 young adults between the ages of 18 and 35 and 40 older adults between the ages of 60 and 80.

First, the researchers administered a series of cognitive tests, like the California Verbal Learning Test (CVLT) and the Trail Making Test (TMT). Seventeen members of the older group scored at or above the mean scores of the younger group. That is, these 17 could be considered super-agers, performing at the same level as the younger study participants. Aside from these individuals, members of the older group tended to perform less well on the cognitive tests. Then, the researchers scanned all participants' brains in an fMRI, paying special attention to two portions of the brain: the default mode network and the salience network.

The default mode network is, as its name might suggest, a series of brain regions that are active by default — when we're not engaged in a task, they tend to show higher levels of activity. It also appears to be very related to thinking about one's self, thinking about others, as well as aspects of memory and thinking about the future.

The salience network is another network of brain regions, so named because it appears deeply linked to detecting and integrating salient emotional and sensory stimuli. (In neuroscience, saliency refers to how much an item "sticks out"). Both of these networks are also extremely important to overall cognitive function, and in super-agers, the activity in these networks was more coordinated than in their peers.

Default Mode Network

Wikimedia Commons

An image of the brain highlighting the regions associated with the default mode network.

How to ensure brain health in old age

While prior research has identified some genetic influences on how "gracefully" the brain ages, there are likely activities that can encourage brain health. "We hope to identify things we can prescribe for people that would help them be more like a superager," said Bradford Dickerson, one of the researchers in this study, in a statement. "It's not as likely to be a pill as more likely to be recommendations for lifestyle, diet, and exercise. That's one of the long-term goals of this study — to try to help people become superagers if they want to."

To date, there is some preliminary evidence of ways that you can keep your brain younger longer. For instance, more education and a cognitively demanding job predicts having higher cognitive abilities in old age. Generally speaking, the adage of "use it or lose it" appears to hold true; having a cognitively active lifestyle helps to protect your brain in old age. So, it might be tempting to fill your golden years with beer and reruns of CSI, but it's unlikely to help you keep your edge.

Aside from these intuitive ways to keep your brain healthy, regular exercise appears to boost cognitive health in old age, as Dickinson mentioned. Diet is also a protective factor, especially for diets delivering omega-3 fatty acids (which can be found in fish oil), polyphenols (found in dark chocolate!), vitamin D (egg yolks and sunlight), and the B vitamins (meat, eggs, and legumes). There's also evidence that having a healthy social life in old age can protect against cognitive decline.

For many, the physical decline associated with old age is an expected side effect of a life well-lived. But the idea that our intellect will also degrade can be a much scarier reality. Fortunately, the existence of super-agers shows that at the very least, we don't have to accept cognitive decline without a fight.


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We have a new range of skills coming to Big Think Edge this week, including communication, critical thinking, and emotional intelligence.

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