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Ask Ethan: How Can LISA, Without Fixed-Length Arms, Ever Detect Gravitational Waves?

“LIGO works by having these exquisitely precise lasers, reflected down perfectly length-calibrated paths, to detect these tiny changes in distance (less than the width of a proton) induced by a passing gravitational wave. With LISA, we plan on having three independent, untethered spacecrafts freely-floating in space. They’ll be affected by all sorts of phenomena, from gravity to radiation to the solar wind. How can we possibly get a gravitational wave signal out of this?”

Imagine you’ve got three spacecrafts, separated by 5 million kilometers apiece, orbiting in empty space behind the Earth. They’re affected by gravity, the pressure from solar radiation, the solar wind, cosmic rays, and literally everything that passes through their environment. Here on Earth, gravitational wave detectors, and the laser arms that allow us to build them, are kept at a fixed length, with gravitational waves causing those arms to expand and contract. In space, there is nothing to “fix” these distances.

So how will LISA ever possibly do this? How will it see a signal against the tremendous backdrop of noise? Find out on this edition of Ask Ethan!

nasa

A Mesmerizing Model of Monster Black Holes

Just about every galaxy the size of our Milky Way (or bigger) has a supermassive black hole at its center. These objects are ginormous — hundreds of thousands to billions of times the mass of the Sun! Now, we know galaxies merge from time to time, so it follows that some of their black holes should combine too. But we haven’t seen a collision like that yet, and we don’t know exactly what it would look like.

A new simulation created on the Blue Waters supercomputer — which can do 13 quadrillion calculations per second, 3 million times faster than the average laptop — is helping scientists understand what kind of light would be produced by the gas around these systems as they spiral toward a merger.

The new simulation shows most of the light produced around these two black holes is UV or X-ray light. We can’t see those wavelengths with our own eyes, but many telescopes can. Models like this could tell the scientists what to look for.

You may have spotted the blank circular region between the two black holes. No, that’s not a third black hole. It’s a spot that wasn’t modeled in this version of the simulation. Future models will include the glowing gas passing between the black holes in that region, but the researchers need more processing power. The current version already required 46 days!

The supermassive black holes have some pretty nifty effects on the light created by the gas in the system. If you view the simulation from the side, you can see that their gravity bends light like a lens. When the black holes are lined up, you even get a double lens!

But what would the view be like from between two black holes? In the 360-degree video above, the system’s gas has been removed and the Gaia star catalog has been added to the background. If you watch the video in the YouTube app on your phone, you can moved the screen around to explore this extreme vista. Learn more about the new simulation here.

Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com.

wonders-of-the-cosmos

Superfluidity consists of an anomalous liquid state of quantum nature which is under a very low temperature behaving as if it had no viscosity and exhibiting an abnormally high heat transfer. This phenomenon was observed for the first time in liquid helium and has applications not only in theories about liquid helium but also in astrophysics and theories of quantum gravitation.

Helium only ends boiling at 2.2 K and is when it becomes helium-II (superfluid helium), getting a thermal conductivity increased by a million times, in addition to becoming a superconductor. Its viscosity tends to zero, hence, if the liquid were placed in a cubic container it would spread all over the surface. Thus, the liquid can flow upwards, up the walls of the container. If the viscosity is zero, the flexibility of the material is non-existent and the propagation of waves on the material occurs under infinite velocity.

Because it is a noble gas, helium exhibits little intermolecular interaction. The interactions that it presents are the interactions of Van der Waals. As the relative intensity of these forces is small, and the mass of the two isotopes of helium is small, the quantum effects, usually disguised under the thermal agitation, begin to appear, leaving the liquid in a state in which the particles behave jointly, under effect of a single wave function. In the two liquids in which cases of superfluidity are known, that is, in isotopes 3 and 4 of helium, the first is composed of fermions whereas the second is composed of bosons. In both cases, the explanation requires the existence of bosons. In the case of helium-3, the fermions group in pairs, similar to what happens in the superconductivity with the Cooper pairs, to form bosons.

Helium’s liquidity at low temperatures allows it to carry out a transformation called Bose–Einstein condensation, in which individual particles overlap until they behave like one big particle.

Superfluid in astrophysics

The idea of superfluids existed within neutron stars was proposed by Russian physicist Arkady Migdal in 1959. Making an analogy with Cooper pairs that form within superconductors, it is expected that protons and neutrons in the nucleus of a star of neutrons with sufficient high pressure and low temperature behave in a similar way forming pairs of Cooper and generate the phenomena of superfluidity and superconductivity.

The existence of this phenomenon was proven by NASA in 2011 when analyzing the neutron star left by supernova Cassiopeia A.

sources: 1, 2, 3 & 4 animation: 1 & 2

startswithabang

What Was It Like When The Universe Made Its First Elements?

“The Universe does form elements immediately after the Big Bang, but almost all of what it forms is either hydrogen or helium. There’s a tiny, tiny amount of lithium left over from the Big Bang, since beryllium-7 decays into lithium, but it’s less than 1-part-in-a-billion by mass. When the Universe cools down enough that electrons can bind to these nuclei, we’ll have our first elements: the ingredients that the very first generations of stars will be made out of.

But they won’t be made out of the elements we think of as essential to existence, including carbon, nitrogen, oxygen, silicon and more. Instead, it’s just hydrogen and helium, to the 99.9999999% level. It took less than four minutes to go from the start of the hot Big Bang to the first stable atomic nuclei, all amidst a bath of hot, dense, expanding-and-cooling radiation. The cosmic story that would lead to us has, in truth, finally begun.”

The first stars wouldn’t form until somewhere between 50 and 100 million years after the Big Bang, but the elements that made them up were created in just the first 3-to-4 minutes. When the Universe was a fraction of a second old, there was a 50/50 split between protons and neutrons; when it was 3 seconds old, it was more like 85/15. But all of those protons and neutrons couldn’t just fuse together to form deuterium, helium, and then the heavier elements like they do in stars, even though the Universe was energetic and dense enough to make that happen.

Instead, we wound up with just hydrogen, helium, and less than 0.0000001% anything else. This is the story of how.

startswithabang

What Was It Like When We Lost The Last Of Our Antimatter?

“The Cosmic Microwave Background’s temperature was first measured to this precision back in 1992, with the first data release of NASA’s COBE satellite. But the neutrino background imprints itself in a very subtle way, and wasn’t detected until 2015. When it was finally discovered, the scientists who did the work found a phase shift in the Cosmic Microwave Background’s fluctuations that enabled them to determine, if neutrinos were massless today, how much energy they’d have at this early time.

Their results? The Cosmic Neutrino Background had an equivalent temperature of 1.96 ± 0.02 K, in perfect agreement with the Big Bang’s predictions.”

Throughout the very early Universe, space was filled with matter and antimatter, which spontaneously self-create from pure Energy via Einstein’s famous E = mc^2. However, as the Universe cools and expands, less energy becomes available to make new particles and antiparticles. Quarks, muons, taus, baryons, mesons, and gauge bosons all are gone by time the Universe is just 25 microseconds old. But positrons, the counterpart of antielectrons, remain until the Universe is a full 3 seconds old! Their existence leads to a crazy prediction: that there should be a cosmic neutrino background at a different temperature from the cosmic microwave background: 1.95 K instead of 2.73 K.

We have verified this, and hence, one of the Big Bang’s craziest predictions, with data collected 13.8 billion years onward! Come learn what it was like when the Universe lost the last of its antimatter.

startswithabang

What Was It Like When The Universe First Created More Matter Than Antimatter?

“This is only one of three known, viable scenarios that could lead to the matter-rich Universe we inhabit today, with the other two involving new neutrino physics or new physics at the electroweak scale, respectively. Yet in all cases, it’s the out-of-equilibrium nature of the early Universe, which creates everything allowable at high energies and then cools to an unstable state, which enables the creation of more matter than antimatter. We can start with a completely symmetric Universe in an extremely hot state, and just by cooling and expanding, wind up with one that becomes matter-dominated. The Universe didn’t need to be born with an excess of matter over antimatter; the Big Bang can spontaneously make one from nothing. The only open question, exactly, is how.”

One of the biggest unsolved questions in physics today is how the Universe came to be filled with matter and not antimatter. After all, the laws of physics are completely matter-antimatter symmetric, and yet when we look at what we have today, every planet, star, and galaxy is made of matter and not antimatter. How did it come to be this way? The young, hot, but rapidly expanding-and-cooling Universe gives us all the ingredients we need for this to occur. We are certain of the exact mechanism, but theoretically, there are some enticing possibilities. Here’s a walk through one of those scenarios in great detail, but expressed so simply that even someone with no physics knowledge can follow it.

Here’s what the Universe was like when it was matter-antimatter symmetric, along with how it could have become matter-rich without breaking the laws of physics.

wonders-of-the-cosmos

What is an Exoplanet?

An exoplanet or extrasolar planet is a planet outside our solar system that orbits a star. The first evidence of an exoplanet was noted as early as 1917, but was not recognized as such. However, the first scientific detection of an exoplanet was in 1988. Shortly afterwards, the first confirmed detection was in 1992. As of 1 April 2018, there are 3,758 confirmed planets in 2,808 systems, with 627 systems having more than one planet.

The High Accuracy Radial Velocity Planet Searcher (HARPS, since 2004) has discovered about a hundred exoplanets while the Kepler space telescope (since 2009) has found more than two thousand. Kepler has also detected a few thousand candidate planets, of which about 11% may be false positives.

In several cases, multiple planets have been observed around a star. About 1 in 5 Sun-like stars have an “Earth-sized” planet in the habitable zone. Assuming there are 200 billion stars in the Milky Way, one can hypothesize that there are 11 billion potentially habitable Earth-sized planets in the Milky Way, rising to 40 billion if planets orbiting the numerous red dwarfs are included.

The least massive planet known is Draugr (also known as PSR B1257+12 A or PSR B1257+12 b), which is about twice the mass of the Moon. The most massive planet listed on the NASA Exoplanet Archive is HR 2562 b, about 30 times the mass of Jupiter, although according to some definitions of a planet, it is too massive to be a planet and may be a brown dwarf instead.

There are planets that are so near to their star that they take only a few hours to orbit and there are others so far away that they take thousands of years to orbit.

Some are so far out that it is difficult to tell whether they are gravitationally bound to the star. Almost all of the planets detected so far are within the Milky Way. Nonetheless, evidence suggests that extragalactic planets, exoplanets further away in galaxies beyond the local Milky Way galaxy, may exist. The nearest exoplanet is Proxima Centauri b, located 4.2 light-years (1.3 parsecs) from Earth and orbiting Proxima Centauri, the closest star to the Sun.

Besides exoplanets, there are also rogue planets, which do not orbit any star and which tend to be considered separately, especially if they are gas giants, in which case they are often counted, like WISE 0855−0714, as sub-brown dwarfs. The rogue planets in the Milky Way possibly number in the billions (or more).

Some planets orbit one member of a binary star system, and several circumbinary planets have been discovered which orbit around both members of binary star. A few planets in triple star systems are known and one in the quadruple system Kepler-64.

Methods of detecting exoplanets

1° Radial velocity

A star with a planet will move in its own small orbit in response to the planet’s gravity. This leads to variations in the speed with which the star moves toward or away from Earth, i.e. the variations are in the radial velocity of the star with respect to Earth. The radial velocity can be deduced from the displacement in the parent star’s spectral lines due to the Doppler effect. The radial-velocity method measures these variations in order to confirm the presence of the planet using the binary mass function.

2º Transit photometry

While the radial velocity method provides information about a planet’s mass, the photometric method can determine the planet’s radius. If a planet crosses (transits) in front of its parent star’s disk, then the observed visual brightness of the star drops by a small amount; depending on the relative sizes of the star and the planet.

3° Direct Imaging

Exoplanets are far away, and they are millions of times dimmer than the stars they orbit. So, unsurprisingly, taking pictures of them the same way you’d take pictures of, say Jupiter or Venus, is exceedingly hard.

New techniques and rapidly-advancing technology are making it happen.

The major problem astronomers face in trying to directly image exoplanets is that the stars they orbit are millions of times brighter than their planets. Any light reflected off of the planet or heat radiation from the planet itself is drowned out by the massive amounts of radiation coming from its host star. It’s like trying to find a flea in a lightbulb, or a firefly flitting around a spotlight.

On a bright day, you might use a pair of sunglasses, or a car’s sun visor, or maybe just your hand to block the glare of the sun so that you can see other things.

This is the same principle behind the instruments designed to directly image exoplanets. They use various techniques to block out the light of stars that might have planets orbiting them. Once the glare of the star is reduced, they can get a better look at objects around the star that might be exoplanets.

4° Gravitational Microlensing

Gravitational microlensing occurs when the gravitational field of a star acts like a lens, magnifying the light of a distant background star. This effect occurs only when the two stars are almost exactly aligned. Lensing events are brief, lasting for weeks or days, as the two stars and Earth are all moving relative to each other. More than a thousand such events have been observed over the past ten years.

If the foreground lensing star has a planet, then that planet’s own gravitational field can make a detectable contribution to the lensing effect. Since that requires a highly improbable alignment, a very large number of distant stars must be continuously monitored in order to detect planetary microlensing contributions at a reasonable rate. This method is most fruitful for planets between Earth and the center of the galaxy, as the galactic center provides a large number of background stars.

5° Astrometry

This method consists of precisely measuring a star’s position in the sky, and observing how that position changes over time. Originally, this was done visually, with hand-written records. By the end of the 19th century, this method used photographic plates, greatly improving the accuracy of the measurements as well as creating a data archive. If a star has a planet, then the gravitational influence of the planet will cause the star itself to move in a tiny circular or elliptical orbit.

Effectively, star and planet each orbit around their mutual centre of mass (barycenter), as explained by solutions to the two-body problem. Since the star is much more massive, its orbit will be much smaller. Frequently, the mutual centre of mass will lie within the radius of the larger body. Consequently, it is easier to find planets around low-mass stars, especially brown dwarfs.

source

source (+ Methods of detecting exoplanets)

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images: NASA/ESA, ESO

animations: x, x, x, x, x

+ Exoplanets

Some intriguing exoplanets

truecrimerip

World renowned physicist Stephen Hawking has died at the age of 76

The British scientist was famed for his work with black holes and relativity, and wrote several popular science books including ‘A Brief History of Time’. At the age of 22 Prof Hawking was given only a few years to live after being diagnosed with a rare form of motor neurone disease. In his 2013 memoir he described how he felt when first diagnosed with motor neurone disease. “I felt it was very unfair - why should this happen to me,” he wrote. “At the time, I thought my life was over and that I would never realise the potential I felt I had. But now, 50 years later, I can be quietly satisfied with my life.”

wonders-of-the-cosmos

Vela Pulsar

The star of this movie is the Vela pulsar, a neutron star that was formed when a massive star collapsed. The Vela pulsar is about 1,000 light years from Earth, spans about 12 miles in diameter, and makes over 11 complete rotations every second, faster than a helicopter rotor. As the pulsar whips around, it spews out a jet of charged particles that race out along the pulsar’s rotation axis at about 70% of the speed of light. In this still image from the movie, the location of the pulsar and the 0.7-light-year-long jet are labeled.

Credit: NASA, Chandra, CXC, Univ of Toronto, M.Durant et al

wonders-of-the-cosmos

Hey! Just wondering, how did a solar eclipse prove the theory of relativity?

According to the theory of relativity space is not static. The movements of objects can change the structure of space.

In Einstein’s view, space is combined with another dimension - time - which creates universewide “fabric” called space-time. Object travel through this fabric, which can be warped, bent and twisted by the masses and motions of objects within space-time.

One prediction of general relativity was that light should not travel in a perfectly straight line. When traveling through space-time and approaching the gravitational field of a mass object, the light must bend-but not too much.

Then the English astronomer Sir Frank Watson Dyson proposed that the total solar eclipse of 1919 could prove, because the Sun would cross the bright Hyades star cluster. Star light would have to cross the gravitational field of the sun on the way to Earth, but would be visible due to the darkness of the eclipse. This would allow precise measurements of the positions displaced by the gravity of the stars in the sky.

Because of this, teams of researchers strategically positioned themselves in two locations that would initially provide the best conditions for observing the eclipse. One group stayed in Ilha do Príncipe, in São Tomé and Príncipe, and other researchers settled in Sobral, Ceará (Brazil).

Eddington, who led the experiment, first measured the “true” positions of the stars during January and February of 1919. In May, he went to remote Prince Island (in the Gulf of Guinea, on the west coast of Africa) to measure Positions of the stars during the eclipse, seen through the gravitational lens of the sun.

The total eclipse lasted about 6 minutes and 51 seconds, during those few minutes the astronomers captured several photos of the total eclipse. When Eddington returned to England, his data from Príncipe confirmed Einstein’s predictions.Eddington announced his discoveries on November 6, 1919.

Images: x ,x ,x ,x

startswithabang

Ask Ethan: What’s The Quantum Reason That Sodium And Water React?

“Which forces drive chemical reactions, and what takes place on a quantum level? In particular, what happens when water interacts with sodium?”

Every beginning chemistry student learns what happens when you put a chunk of sodium metal into water: you get an extremely violent reaction out. The sodium and water bubble and fizz, and sometimes even a flame or an outright combustion reaction is produced. This isn’t exclusive to sodium, either, but occurs for lithium, potassium, rubidium, cesium and more. We can describe these chemical reactions using basic chemistry, of course, but there’s a more fundamental reason it occurs: the laws of quantum mechanics. By combining the laws of electromagnetism with the Pauli exclusion principle and the shapes of electron orbitals, we can understand the full step-by-step process by which this occurs. Thanks to these laws, a reaction that had been described for hundreds of years can now finally be fully explained.

What’s the quantum reason sodium and water react? Find out on this edition of Ask Ethan!

spaceplasma

Coronal Prominence Cavity

Prominences are regions of cool, condensed plasma supported by twisted magnetic field lines that globally wrap around an axial magnetic field, called a magnetic flux rope. Most of the flux rope volume is filled with depleted coronal plasma and forms a transitory cavity – a dark elliptical or semi-circular region that appears empty from our viewpoint. White-light coronagraph observations suggest that cavity density is approximately half the density of the surrounding streamers. However, the plasma properties within the cavities are not uniform, they exhibit temperature substructures that have been observed in multiple wavelengths.

Tuned to observe emission in the extreme ultraviolet (EUV or XUV), NASA’s Atmospheric Imaging Assembly (AIA) instrument on board the Solar Dynamics Observatory (SDO) provides high-definition imagery of the Sun in seven wavelength passbands. Each of the wavelengths highlight a specific aspect of the solar surface and atmosphere, for example; the dark elliptical structure of the coronal cavity, and outer bright streamers are most visible in AIA 211 Å (Fe XIV), and AIA 193 Å (Fe XII, XXIV) channels, as shown below: