When Dead Stars Collide!

Gravity has been making waves - literally.  Earlier this month, the Nobel Prize in Physics was awarded for the first direct detection of gravitational waves two years ago. But astronomers just announced another huge advance in the field of gravitational waves - for the first time, we’ve observed light and gravitational waves from the same source.

There was a pair of orbiting neutron stars in a galaxy (called NGC 4993). Neutron stars are the crushed leftover cores of massive stars (stars more than 8 times the mass of our sun) that long ago exploded as supernovas. There are many such pairs of binaries in this galaxy, and in all the galaxies we can see, but something special was about to happen to this particular pair.

Each time these neutron stars orbited, they would lose a teeny bit of gravitational energy to gravitational waves. Gravitational waves are disturbances in space-time - the very fabric of the universe - that travel at the speed of light. The waves are emitted by any mass that is changing speed or direction, like this pair of orbiting neutron stars. However, the gravitational waves are very faint unless the neutron stars are very close and orbiting around each other very fast.

As luck would have it, the teeny energy loss caused the two neutron stars to get a teeny bit closer to each other and orbit a teeny bit faster.  After hundreds of millions of years, all those teeny bits added up, and the neutron stars were *very* close. So close that … BOOM! … they collided. And we witnessed it on Earth on August 17, 2017.  

Credit: National Science Foundation/LIGO/Sonoma State University/A. Simonnet

A couple of very cool things happened in that collision - and we expect they happen in all such neutron star collisions. Just before the neutron stars collided, the gravitational waves were strong enough and at just the right frequency that the National Science Foundation (NSF)’s Laser Interferometer Gravitational-Wave Observatory (LIGO) and European Gravitational Observatory’s Virgo could detect them. Just after the collision, those waves quickly faded out because there are no longer two things orbiting around each other!

LIGO is a ground-based detector waiting for gravitational waves to pass through its facilities on Earth. When it is active, it can detect them from almost anywhere in space.

The other thing that happened was what we call a gamma-ray burst. When they get very close, the neutron stars break apart and create a spectacular, but short, explosion. For a couple of seconds, our Fermi Gamma-ray Telescope saw gamma-rays from that explosion. Fermi’s Gamma-ray Burst Monitor is one of our eyes on the sky, looking out for such bursts of gamma-rays that scientists want to catch as soon as they’re happening.

And those gamma-rays came just 1.7 seconds after the gravitational wave signal. The galaxy this occurred in is 130 million light-years away, so the light and gravitational waves were traveling for 130 million years before we detected them.

After that initial burst of gamma-rays, the debris from the explosion continued to glow, fading as it expanded outward. Our Swift, HubbleChandra and Spitzer telescopes, along with a number of ground-based observers, were poised to look at this afterglow from the explosion in ultraviolet, optical, X-ray and infrared light. Such coordination between satellites is something that we’ve been doing with our international partners for decades, so we catch events like this one as quickly as possible and in as many wavelengths as possible.

Astronomers have thought that neutron star mergers were the cause of one type of gamma-ray burst - a short gamma-ray burst, like the one they observed on August 17. It wasn’t until we could combine the data from our satellites with the information from LIGO/Virgo that we could confirm this directly.

This event begins a new chapter in astronomy. For centuries, light was the only way we could learn about our universe. Now, we’ve opened up a whole new window into the study of neutron stars and black holes. This means we can see things we could not detect before.

The first LIGO detection was of a pair of merging black holes. Mergers like that may be happening as often as once a month across the universe, but they do not produce much light because there’s little to nothing left around the black hole to emit light. In that case, gravitational waves were the only way to detect the merger.

Image Credit: LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)

The neutron star merger, though, has plenty of material to emit light. By combining different kinds of light with gravitational waves, we are learning how matter behaves in the most extreme environments. We are learning more about how the gravitational wave information fits with what we already know from light - and in the process we’re solving some long-standing mysteries!

Want to know more? Get more information HERE.

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Northern California Fires

As many of you know I am attending University, I never specified which university for privacy reasons. I attend Sonoma State. My university is some 20 minutes from Santa Rosa. If you’ve been watching the news Santa Rosa is on fire. Yesterday morning I woke up to my roommates freaking out about the fire and being told the fire was 2 miles from us. The school told us we didn’t have to evacuate if we didn’t want to. My heart started racing. I felt like my heart was going to jump out of my chest. My first thought was I need to go home and I was ready to grab my car keys and leave in my pajamas and slippers. The fact that I had roommates didn’t cross my mind. I said I’m going home and they looked at me and I realized they’re just as scared as me, I can’t leave them behind. I called my parents and my dad managed to book us a hotel in Vallejo, an hour from the fire. We packed overnight bags and jumped in my car 15 mins later. It was hell trying to leave Rohnert Park. One of my roommates was giving us a hard time, she wanted us to leave her at a church that was being used as a evacuation center. I agreed to leave her there but told her she needed to call her dad and tell her where she was. On the way to the church, we got stuck in crazy traffic. Roads were being closed right and left and we were being rerouted, so I told her that I was taking her with us to Vallejo. She got upset and called her dad to complain, I was driving but let me tell you I wanted to yell at her. I’m freaking out and so is everyone else, I am taking you to safety and you want to complain about it! Our other roommate told her to let her talk to her dad and she explained why we were taking her to Vallejo and he agreed that is was better to get out now and stay together. She grew upset and posted about it on facebook and kept calling her dad. I managed to get onto a backroad and was able to get us out of Rohnert Park before they shut down the roads. We’re some 8 minutes from Vallejo and her dad tells us to take her back to the church. I told her no. She’s like but my dad said to. I told her I’m 8 minutes from Vallejo, if he wants you he can come get you, I’m not driving us back there. She sulks the rest of the time texting her dad and posting it on facebook. I have never been so frustrated with someone in my life. I honestly think my frustration with her kept me from having a panic attack.. The rest of this will be continued later. 

San Marcos or Sonoma?

No idea which one to pick.

San Marcos would mean staying at home and having the support of my friends and family.

Sonoma would mean cold rainy northern california, where I know not one person but would have a better college experience.

I have until friday to choose where ill be spending my next four years.

This decision makes me sick to my stomach.

I don’t want high school to end.