What Was It Like When The Universe Made Its Heaviest Elements?
“For a long time, it was speculated that merging neutron stars would provide the origin of these elements, as two massive balls of neutrons smashing together could create an endless variety of heavy atomic nuclei. Sure, most of the mass from these objects would merge together into a final-stage object like a black hole, but a few percent should be ejected as part of the collision.
In 2017, observations made with both telescopes and with gravitational wave observatories confirmed that not only are neutron star mergers responsible for the overwhelming majority of these heavy elements, but that short-period gamma ray bursts can be linked to these mergers as well. Now known as a kilonova, it’s well-understood that neutron star-neutron star mergers are the origin of the majority of the heaviest elements found throughout the Universe.”
For those of you keeping track, this is the 22nd article I’ve written in my “what was it like when…” series. There’s an entire past and future history of our Universe to tell, and we haven’t even reached the present day.
Enjoy the story of how we made the heaviest elements of all, and stay tuned for even more.
The 7 Most Powerful Fireworks Shows In The Universe
“Forget mere chemical reactions; in space, matter-energy conversion creates unprecedentedly powerful explosive events.
Here are the 7 most powerful natural displays of cosmic fireworks.
7.) Type Ia supernova: when two white dwarf stars collide, they initiate a runaway fusion reaction, destroying both stellar remnants.”
Throughout the Universe, there are many beautiful displays of cosmic fireworks. Stars are born; galaxies collide; gas gets heated and expelled; stars and stellar remnants explode and die. We typically think of supernova events as the culmination of the brightest, most energetic things that can happen in the cosmos. But supernovae only fill up the bottom rungs on the list of the most powerful, natural fireworks shows that the Universe provides us with.
Which ones are the most energetic? Find out on this incredible start to your pre-4th-of-July Monday!
LIGO’s Greatest Discovery Almost Didn’t Happen
“If all we had done was look at the automated signals, we would have gotten just one “single-detector alert,” in the Hanford detector, while the other two detectors would have registered no event. We would have thrown it away, all because the orientation was such that there was no significant signal in Virgo, and a glitch caused the Livingston signal to be vetoed. If we left the signal-finding solely to algorithms and theoretical decisions, a 1-in-10,000 coincidence would have stopped us from finding this first-of-its-kind event. But we had scientists on the job: real, live, human scientists, and now we’ve confidently seen a multi-messenger signal, in gravitational waves and electromagnetic light, for the very first time.”
Imagine the scene: it’s mid-August, 2017, and the Virgo detector has just joined the twin LIGO detectors barely two weeks ago. Amazingly, on August 14th, you’ve seen a gravitational wave signal in all three detectors; another black hole-black hole merger. Then, all of a sudden, even though the LIGO detectors are set to shut down later in the month, an extraordinarily significant signal goes off… but only in one detector. The LIGO Hanford detector sees a signal with a false-alarm probability of just one part in 300 billion; a slam dunk. Yet both LIGO Livingston and Virgo see nothing. A non-coincident signal should automatically be rejected, but somehow, one of the young researchers working on the project thought to check the Livingston data by hand… and that was where the secret lay.
LIGO’s greatest discovery, of two merging neutron stars, almost was overlooked. Thankfully, the hands-on nature of the scientists working on gravitational waves were able to turn this into the discovery of the century! (So far!)
Why Neutron Stars, Not Black Holes, Show The Future Of Gravitational Wave Astronomy
“3.) Gravitational waves move at exactly the speed of light! Before this detection, we never had a gravitational wave and a light signal simultaneously identifiable to compare with one another. After a journey of 130 million light years, the first electromagnetic signal from this detection arrived just 1.7 seconds after the peak of the gravitational wave signal. That means, at most, the difference between the speed of gravity and the speed of light is about 0.12 microns-per-second, or 0.00000000000004%. It’s anticipated that these two speeds are exactly equal, and the delay of the light signal comes from the fact that the light-producing reactions in the neutron star take a second or two to reach the surface.”
Detecting black holes and the gravitational wave signals from them was an incredible feat, but doing the same thing for neutron star mergers is a true game-changer. Instead of fractions of a second, neutron star mergers show up for up to half a minute. Unlike black holes, there’s an electromagnetic counterpart. Because of that, we can verify that the speed of gravity really is identical to the speed of light: to better than 1 part in 1,000,000,000,000,000. And perhaps most spectacularly, we can bring the electromagnetic and gravitational-wave skies together for the first time. Even though LIGO has seen more merging black holes, the fact is that there are more merging neutron stars. The key, now, is finding them. We live at a moment where gravitational wave astronomy is just in its infancy, giving us a whole new way to look at the Universe.
For the first time, we’re doing it. Here’s the incredible science of what we’re actually learning, and what the future of gravitational wave + electromagnetic astronomy now holds.