Gravitational Lens Archives

June 18, 2017 by Fraser Cain

Gravitational Astronomy? How Detecting Gravitational Waves Changes Everything

Just a couple of weeks ago, astronomers from Caltech announced their third detection of gravitational waves from the Laser Interferometer Gravitational-Wave Observatory or LIGO.

As with the previous two detections, astronomers have determined that the waves were generated when two intermediate-mass black holes slammed into each other, sending out ripples of distorted spacetime.

One black hole had 31.2 times the mass of the Sun, while the other had 19.4 solar masses. The two spiraled inward towards each other, until they merged into a single black hole with 48.7 solar masses. And if you do the math, twice the mass of the Sun was converted into gravitational waves as the black holes merged.

On January 4th, 2017, LIGO detected two black holes merging into one. Courtesy Caltech/MIT/LIGO Laboratory

These gravitational waves traveled outward from the colossal collision at the speed of light, stretching and compressing spacetime like a tsunami wave crossing the ocean until they reached Earth, located about 2.9 billion light-years away.

The waves swept past each of the two LIGO facilities, located in different parts of the United States, stretching the length of carefully calibrated laser measurements. And from this, researchers were able to detect the direction, distance and strength of the original merger.

Seriously, if this isn’t one of the coolest things you’ve ever heard, I’m clearly easily impressed.

Now that the third detection has been made, I think it’s safe to say we’re entering a brand new field of gravitational astronomy. In the coming decades, astronomers will use gravitational waves to peer into regions they could never see before.

Being able to perceive gravitational waves is like getting a whole new sense. It’s like having eyes and then suddenly getting the ability to perceive sound.

This whole new science will take decades to unlock, and we’re just getting started.

As Einstein predicted, any mass moving through space generates ripples in spacetime. When you’re just walking along, you’re actually generating tiny ripples. If you can detect these ripples, you can work backwards to figure out what size of mass made the ripples, what direction it was moving, etc.

Even in places that you couldn’t see in any other way. Let me give you a couple of examples.

Black holes, obviously, are the low hanging fruit. When they’re not actively feeding, they’re completely invisible, only detectable by how they gravitational attract objects or bend light from objects passing behind them.

But seen in gravitational waves, they’re like ships moving across the ocean, leaving ripples of distorted spacetime behind them.

With our current capabilities through LIGO, astronomers can only detect the most massive objects moving at a significant portion of the speed of light. A regular black hole merger doesn’t do the trick – there’s not enough mass. Even a supermassive black hole merger isn’t detectable yet because these mergers seem to happen too slowly.

LIGO has already significantly increased the number of black holes with known masses. The observatory has definitively detected two sets of black hole mergers (bright blue). For each event, LIGO determined the individual masses of the black holes before they merged, as well as the mass of the black hole produced by the merger. The black holes shown with a dotted border represent a LIGO candidate event that was too weak to be conclusively claimed as a detection. Credit: LIGO/Caltech/Sonoma State (Aurore Simonnet)

This is why all the detections so far have been intermediate-mass black holes with dozens of times the mass of our Sun. And we can only detect them at the moment that they’re merging together, when they’re generating the most intense gravitational waves.

If we can boost the sensitivity of our gravitational wave detectors, we should be able to spot mergers of less and more massive black holes.

But merging isn’t the only thing they do. Black holes are born when stars with many more times the mass of our Sun collapse in on themselves and explode as supernovae. Some stars, we’ve now learned just implode as black holes, never generating the supernovae, so this process happens entirely hidden from us.

Is there a singularity at the center of a black hole event horizon, or is there something there, some kind of object smaller than a neutron star, but bigger than an infinitely small point? As black holes merge together, we could see beyond the event horizon with gravitational waves, mapping out the invisible region within to get a sense of what’s going on down there.

This illustration shows the merger of two black holes and the gravitational waves that ripple outward as the black holes spiral toward each other. In reality, the area near the black holes would appear highly warped, and the gravitational waves would be difficult to see directly. Credit: LIGO/T. Pyle

We want to know about even less massive objects like neutron stars, which can also form from a supernova explosion. These neutron stars can orbit one another and merge generating some of the most powerful explosions in the Universe: gamma ray bursts. But do neutron stars have surface features? Different densities? Could we detect a wobble in the gravitational waves in the last moments before a merger?

And not everything needs to merge. Sensitive gravitational wave detectors could sense binary objects with a large imbalance, like a black hole or neutron star orbiting around a main sequence star. We could detect future mergers by their gravitational waves.

Are gravitational waves a momentary distortion of spacetime, or do they leave some kind of permanent dent on the Universe that we could trace back? Will we see echoes of gravity from gravitational waves reflecting and refracting through the fabric of the cosmos?

Perhaps the greatest challenge will be using gravitational waves to see beyond the Cosmic Microwave Background Radiation. This region shows us the Universe 380,000 years after the Big Bang, when everything was cool enough for light to move freely through the Universe.

But there was mass there, before that moment. Moving, merging mass that would have generated gravitational waves. As we explained in a previous article, astronomers are working to find the imprint of these gravitational waves on the Cosmic Microwave Background, like an echo, or a shadow. Perhaps there’s a deeper Cosmic Gravitational Background Radiation out there, one which will let us see right to the beginning of time, just moments after the Big Bang.

And as always, there will be the surprises. The discoveries in this new field that nobody ever saw coming. The “that’s funny” moments that take researchers down into whole new fields of discovery, and new insights into how the Universe works.

The Laser Interferometer Gravitational-Wave Observatory (LIGO)facility in Livingston, Louisiana. The other facility is located in Hanford, Washington. Image: LIGO — The Laser Interferometer Gravitational-Wave Observatory (LIGO) facility in Livingston, Louisiana. The other facility is located in Hanford, Washington. Image: LIGO

The LIGO project was begun back in 1994, and the first iteration operated from 2002 to 2012 without a single gravitational wave detection. It was clear that the facility wasn’t sensitive enough, so researchers went back and made massive improvements.

In 2008, they started improving the facility, and in 2015, Advanced LIGO came online with much more sensitivity. With the increased capabilities, Advanced LIGO made its first discovery in 2016, and now two more discoveries have been added.

LIGO can currently only detect the general hemisphere of the sky where a gravitational wave was emitted. And so, LIGO’s next improvement will be to add another facility in India, called INDIGO. In addition to improving the sensitivity of LIGO, this will give astronomers three observations of each event, to precisely detect the origin of the gravitational waves. Then visual astronomers could do follow up observations, to map the event to anything in other wavelengths.

Current operating facilities in the global network include the twin LIGO detectors—in Hanford, Washington, and Livingston, Louisiana—and GEO600 in Germany. The Virgo detector in Italy and the Kamioka Gravitational Wave Detector (KAGRA) in Japan are undergoing upgrades and are expected to begin operations in 2016 and 2018, respectively. A sixth observatory is being planned in India. Having more gravitational-wave observatories around the globe helps scientists pin down the locations and sources of gravitational waves coming from space. Image made in February 2016. Credit: Caltech/MIT/LIGO Lab

A European experiment known as Virgo has been operating for a few years as well, agreeing to collaborate with the LIGO team if any detections are made. So far, the Virgo experiment hasn’t found anything, but it’s being upgraded with 10 times the sensitivity, which should be fully operational by 2018.

A Japanese experiment called the Kamioka Gravitational Wave Detector, or KAGRA, will come online in 2018 as well, and be able to contribute to the observations. It should be capable of detecting binary neutron star mergers out to nearly a billion light-years away.

Just with visual astronomy, there are a set of next generation supergravitational wave telescopes in the works, which should come online in the next few decades.

The Europeans are building the Einstein Telescope, which will have detection arms 10 km long, compared to 4 km for LIGO. That’s like, 6 more km.

There’s the European Space Agency’s space-based Laser Interferometer Space Antenna, or LISA, which could launch in 2030. This will consist of a fleet of 3 spacecraft which will maintain a precise distance of 2.5 million km from each other. Compare that to the Earth-based detection distances, and you can see why the future of observations will come from space.

The Laser Interferometer Space Antenna (LISA) consists of three spacecraft orbiting the sun in a triangular configuration. Credit: NASA

And that last idea, looking right back to the beginning of time could be a possibility with the Big Bang Observer mission, which will have a fleet of 12 spacecraft flying in formation. This is still all in the proposal stage, so no concrete date for if or when they’ll actually fly.

Gravitational wave astronomy is one of the most exciting fields of astronomy. This entirely new sense is pushing out our understanding of the cosmos in entirely new directions, allowing us to see regions we could never even imagine exploring before. I can’t wait to see what happens next.

May 20, 2017 by Fraser Cain

Are There Dark Matter Galaxies? ft. Sarah Pearson from Space with Sarah

One of the things I love about astronomy is how it’s rapidly changing and evolving over time. Every day there are new discoveries, and advancements in theories that take us incrementally forward in our understanding of the Universe.

One of the best examples of this is dark matter; mysterious and invisible but a significant part of the Universe and accounting for the vast majority of mass out there.

It was first theorized almost 100 years ago when astronomers surveyed the total mass of distant galaxy clusters and found that the visible mass we can see must be just a fraction of the total material in the clusters. When you add up the stars and gas, galaxies move and rotate in ways that indicate there’s a huge halo of invisible matter surrounding it.

Some of the best evidence came from Vera Rubin and Kent Ford in the 60s and 70s, when they measured the rotational velocity of edge-on spiral galaxies. They estimated that there must be about 6 times as much dark matter as regular matter.

This NASA Hubble Space Telescope image shows the distribution of dark matter in the center of the giant galaxy cluster Abell 1689

Dark matter became a serious mystery in astronomy, and many observers and theorists have spent the last half century trying to work out what it is.

And dark matter hasn’t given up its secrets easily. Originally, astronomers thought it might not actually be invisible mass, but a misunderstanding of how gravity works at the largest scales.

But over the last few decades, techniques have been developed, using the gravity of dark matter itself to measure how it bends light from more distant objects. Astronomers don’t know what dark matter is, but they’re able to use it as a telescope. Now that’s impressive.

They’ve found amazing features in the dark matter web out there, vast walls and filaments defining the largest scale structures in the Universe. Clusters where dark matter and its gas have been separated from each other.

Remember, we are at the cutting edge of this mystery, and you’re watching it unfold in real time. 25 years from now, I’m sure we’ll look back at our quaint attempts to understand dark matter.

One of the most interesting questions I have right now is: could there be dark matter galaxies? Completely invisible to our eyes, but able to interact through gravity?

Dark Matter Distribution in Supercluster Abell 901/902

Of course, in times like this, I like to bring in a ringer. Someone who has dedicated their life to the study of these questions.

And today, I’ve got with my Sarah Pearson, a graduate student in astronomy at Columbia University and the host of “Space with Sarah”. Sarah studies the formation and interactions of dwarf galaxies surrounding the Milky Way to understand how galaxies built up at the earliest times in the Universe and form the large galaxies we see at present day.

Fraser: Sarah, welcome to the Guide to Space.

Sarah: Hi Fraser, thanks.

Fraser: Can you talk a little bit about how astronomers map out the distribution of dark matter in the Universe?

Sarah: Yes, definitely. So that is a hard question, as you just explained, we don’t see the dark matter. But one assumption about the Universe we live in is that the light matter or baryonic matter. For example, what you, me and stars consist of, and also galaxies, kind of trace out where the dark matter is located.

So one assumption is that the light matter follows the dark matter. In that way we can actually map out to huge distances, kind of how galaxies and clusters of galaxies are located in our Universe. And we imagine that the dark matter structure is somewhat similar.

Simulation of dark matter. Image credit: NASA

And also recently, very large scale structure simulations of our own Universe have addressed this by kind of starting out with an almost uniform distribution of dark matter in the very early Universe. And what they see is when they let the Universe evolve in time, for example, when the Universe is expanding, you kind of have these dark matter clumps forming into galaxies in all these filaments that you discussed.

You can kind of trace out the location of dark matter by understanding the expansion of space versus gravity that creates the galaxies that we see.

Fraser: And I know in the observations that you see these different distributions of matter and dark matter, it’s not the perfect 1:6 radio that I just mentioned before. You actually see clumping of dark matter that’s sometimes separated from regular matter. So can you actually have whole galaxies that are entirely made of dark matter?

Sarah: Yes, that’s one of the topics I’m super excited about. I work on some of these dark matter only galaxies, and the way you can think about it is that the dark matter is almost uniformly distributed in the early Universe. But some of it is slightly denser than other parts, which collapses down into galaxies. And a lot of those galaxies will actually be a lot smaller than the Milky Way. And because they’re so small, they have a hard time actually holding onto the matter within them.

A bright young star shines Credit: NASA/JPL-Caltech

We think that when star formation turned on in these galaxies, you might actually blow out a lot of the gas that might create more stars, but you won’t blow out the dark matter. That means you could end up with these small tiny galaxies that only have dark matter. They might have some gas, but they’re very hard for us astronomers to find.

Fraser: Well, if they are dark matter, and the dark matter is invisible, how do we find them?

Sarah: Oh, great question. So for example, around our own galaxy Milky Way, it’s hypothesized in our current paradigm of cosmology and the way we think about the Universe, there should actually be thousands of dark matter clumps, these dark matter galaxies, kind of orbiting our own galaxy.

Artist’s impression of dark matter surrounding the Milky Way. (ESO/L. Calçada)

Some of these might be destroyed when they pass through the huge Milky Way disk, that’s one way of destroying them. The smaller ones might be destroyed just by the tides as they orbit around the galaxy. However, we imagine that some of them might survive. Actually they can plough through what we call stellar streams, which are formed when a real galaxy falls into our own Milky Way and tidally stretched out. You should be able to see these density signatures in the stellar stream, and that might indicate what type of dark matter halo that ploughed through them.

Fraser: You hinted at a way that they could form. You’ve got these stars as they’re early forming and blasting themselves apart and the clump of dark matter can’t hold onto them, so that part is gone. Is that the main way these might form, are there other ways you can get these dark galaxies?

Sarah: A different hypothesis is if you have an AGN, an active galactic nuclei within a galaxy from a black hole, you could actually that way blow out a lot of the gas from a galaxy as well. But it’s still not really clear to us astronomers what type of galaxies and if small galaxies would have these active galactic nuclei.

This artist’s impression shows the surroundings of the supermassive black hole at the heart of the active galaxy NGC 3783 in the southern constellation of Centaurus (The Centaur). Credit: ESO/M. Kornmesser

So the best theory right now is that some of them might have attracted a lot of gas initially because they didn’t have a lot of gravity to pull in the gas. But also, because this gas is completely lost. Also from stars exploding, actually, not just from stars turning on initially.

Fraser: And I know that astronomers and physicists are trying to search for dark matter in the Large Hadron Collider, and try to see if they can understand the underlying particle. Does the search that you’re working on give us any sense of that underlying nature of dark matter?

Sarah: Yeah, also a great question, because for example if dark matter is cold. The cold dark matter paradigm is very popular right now. Which states that dark matter might be a very massive weakly interacting particle. When we’re saying warm or cold dark matter, we’re also referring to how fast it’s moving. And depending on what kind of particle dark matter is, that kind of sets the structure for of the early Universe.

So we can start to count, if we have cold dark matter, we would expect to see a certain amount of these cold dark galaxies, where that amount would be different, if we had warm dark matter.

The international Super Cryogenic Dark Matter Search (SuperCDMS) has detected what may be the particle that’s thought to make up dark matter throughout the Universe.

Fraser: That’s really cool, so the observations that you do give the physicists a better idea of what they should be looking for in their particle accelerators, and the two sides can work together. That’s really great.

Okay Sarah, place your bets. What do you think is the most likely candidate for dark matter?

Sarah: I still think this is a hard question, and I’m not sure if the particle physicists yet think we’re helping them. We’re still approaching things from different sides, but we’ll see.

I still think it’s going to be one of those weakly interactive massive particles that we just haven’t detected yet.

Fraser: Thank you so much for joining me on the Guide to Space Sarah, I really appreciate you explaining these dark matter galaxies to us.

Well there you have it. Dark matter is strange, strange stuff. We still don’t know what it is, but we can see how it moves, interacts with matter through its gravity. And we can see how it can form entire galaxies of just dark matter.

A big thanks to Sarah Pearson. If you haven’t already, go and check out her YouTube channel: Space with Sarah. She’s covering big topics, like wondering when the Sun will shut off, how big the Universe is, and how galaxies can collide in an expanding Universe.

April 25, 2014December 23, 2015 by Elizabeth Howell

Gallery: Incredible Mirages In Space Show Dark Matter, Supernovas And Galaxies

This artist’s impression of a supernova shows the layers of gas ejected prior to the final deathly explosion of a massive star. Credit: NASA/Swift/Skyworks Digital/Dana Berry

How can an exploding star appear far brighter than expected? This question vexed astronomers since the discovery of PS1-10afx, supernova that was about 30 times more luminous than other Type 1A supernovas. Astronomers have just confirmed in Science that it was likely due to well-known illusion in space.

The mirage is called a gravitational lens that happens when a huge object in the foreground (like a galaxy) bends the light of an object in the background. Astronomers use this trick all the time to spy on galaxies and even to map dark matter, the mysterious substance believed to make up most of the universe.

Check out some spectacular images below of the phenomenon in action.

Canada-France-Hawaii-Telescope (CFHT) image of the field before the supernova PS1-10afx. (Credit: Kavli IPMU / CFHT)

Dark matter in the Bullet Cluster. Otherwise invisible to telescopic views, the dark matter was mapped by observations of gravitational lensing of background galaxies. Credit: X-ray: NASA/CXC/CfA/ M.Markevitch et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/ D.Clowe et al. Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.;

Hubble Space Telescope image shows Einstein ring of one of the SLACS gravitational lenses, with the lensed background galaxy enhanced in blue. A. Bolton (UH/IfA) for SLACS and NASA/ESA.

The image is made from HST data and shows the four lensed images of the dusty red quasar, connected by a gravitational arc of the quasar host galaxy. The lensing galaxy is seen in the centre, between the four lensed images. Credit: John McKean/HST Archive data

The HST WFPC2 image of gravitational lensing in the galaxy cluster Abell 2218, indicating the presence of large amount of dark matter (credit Andrew Fruchter at STScI).

A picture of the object J1000+0221, which demonstrates the most distant gravitational lens ever discovered. This Hubble picture shows a normal galaxy's center region (the glow in the picture), but the object is also aligned with a younger, star-creating galaxy that is in behind. The object in the foreground pulls light from the background galaxy with gravity -- making rings of pictures. Credit: NASA/ESA/A. van der Wel — A picture of the object J1000+0221, which demonstrates the most distant gravitational lens ever discovered. This Hubble picture shows a normal galaxy’s center region (the glow in the picture), but the object is also aligned with a younger, star-creating galaxy that is in behind. The object in the foreground pulls light from the background galaxy with gravity — making rings of pictures. Credit: NASA/ESA/A. van der Wel

January 10, 2014December 29, 2015 by Fraser Cain

Weekly Space Hangout – January 10, 2014: Wake Up, Rosetta! & Top Stories from AAS

Host: Fraser Cain
Guests: David Dickinson, Amy Shira Teitel, Scott Lewis, Brian Koberlein, special guest Ruth McAvinia from the ESA

This week’s stories:
Ruth:
Wake up, Rosetta!
Facebook link to contest

David:
AAS-Gamma Ray Gravitational Lens
AAS-Death by Black Hole
Antares Launch
Remote Deployment of Cubesats
Venus at Inferior Conjunction

Scott:
Learning tools for visually impaired:
More information on the 3-D Hubble images can be found here
Here’s the press release for the iBook being released
Frontier Fields

Brian:
New Triple Star System

Amy:
ISS Life extension

Fraser:
Space Ship 2’s first Supersonic Flight

We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Google+, Universe Today, or the Universe Today YouTube page.