Gravitational Astronomy? How Detecting Gravitational Waves Changes Everything

We’ve now had multiple detections of gravitational waves, opening up a whole new field: gravitational astronomy. We talk about the detections made so far, and how we can see the Universe in a whole new way.

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Can We Now Predict When A Neutron Star Will Collapse?

New research indicates that it may now be possible to predict when a neutron star will collapse to form a new black hole. Credit and Copyright: Paramount Pictures/Warner Bros.

A neutron star is perhaps one of the most awe-inspiring and mysterious things in the Universe. Composed almost entirely of neutrons with no net electrical charge, they are the final phase in the life-cycle of a giant star, born of the fiery explosions known as supernovae. They are also the densest known objects in the universe, a fact which often results in them becoming a black hole if they undergo a change in mass.

For some time, astronomers have been confounded by this process, never knowing where or when a neutron star might make this final transformation. But thanks to a recent study by a team of researchers from Goethe University in Frankfurt, Germany, it may now be possible to determine the absolute maximum mass that is required for a neutron star to collapse, giving birth to a new black hole.

As with everything else relating to neutron stars, the process by which they become black holes has long been a source of fascination and bewilderment for astronomers. As the densest of all objects in the known universe, their mass cannot grow without bound – meaning that any increase in mass will also cause an increase in their density.

Normally, this process will cause a neutron star to simply achieve a new state of equilibrium, or will result in a non-rotating neutron star beginning to  spin. This latter effect will allow it to remain stable for longer than it could otherwise, since the additional centrifugal force can help to balance out the intense gravitational force at work in its interior.

However, even this process cannot last forever. As Professor Luciano Rezolla of Goethe University told Universe Today via email:

“If the star is nonrotating, then this mass is not too difficult to compute and is called the maximum nonrotating mass, or M_TOV. However, this is not the largest mass possible because if the star is rotating, it can sustain more mass than if is not rotating. Even in this case, however, there is a limit because there is a limit to how much a star can rotate before being broken apart from the centrifugal force. Hence, the absolute largest mass that a neutron star can achieve is known as the “maximum mass of a maximally rotating configuration”, M_max.  This is the largest possible mass of the most rapidly rotating model. Suppose you have built such a model: if you added a single atom onto it, it would collapse to a black hole, while it would break apart if you spun it a bit more.”

As neutron stars accumulate mass, the speed of their rotation will increase; and here too, there is a limit. Basically, sooner or later, a neutron star will reach its absolute maximum mass and beyond this, it will inevitably collapse in on itself to become a black hole. Unfortunately, in the past, astronomers have had a hard time determining what the value of this limit was.

The reason for this is because such a maximum value is dependent on the equation of state of the matter composing the star. This thermodynamic equation describes the state of matter under a given set of physical conditions – i.e. temperature, pressure, volume, or internal energy. And while astronomers have been able to ascertain within a degree of certainty what the maximum mass of a nonrotating neutron stars would be, they have been less successful in calculating what the maximum mass is for those that are rotating.

In short, they have been unable to determine how much mass is needed before a rotating neutron star will surpass its maximum speed of rotation and finally form a new black hole. As Rezolla explained:

“What made it difficult in the past to calculate M_max is its value will differ from what composes the neutron star (i.e. its “equation of state”) and this is something we don’t really know. Neutron-star matter is so different from the one we know that we can only make educated guesses; and unfortunately, there are many guesses because there are several different ways to compute the properties of the equation of state. So one ended up up with a situation in which not only the maximum mass was different for different equations of state, but even the maximum rotation speed was different for different equations of state.”

However, in their study, titled “Maximum mass, moment of inertia and compactness of relativistic stars” – which appeared recently in the Monthly Notices of the Royal Astronomical SocietyRezzolla and Cosima Breu (a Masters student in theoretical physics at Goethe University and co-author of the study) argue that it may now be possible to infer what the maximum mass of a rapidly rotating star would be.

For the sake of their research, Rezolla and Breu relied on recent work by astronomers that has shown that it is possible to express the properties of stellar equilibrium configurations that does not depend on the specific equation of the state of their mass. In short, these studies have shown that there are certain “universal relations” when it comes to the equilibrium of stars.

As a result, they were able to show that it is possible to predict the maximum mass a rapidly rotating neutron star can attain by simply considering what the maximum mass is of a neutron star in a corresponding, non-rotating configuration. But as Rezolla indicated, even with these data sets available, what was needed was a fresh perspective:

“Universal relations simply state that objects that are apparently different actually share many things in common. For example, although we are different from other mammals, say pigs, our genome has a huge amount of common features, essentially because we have to synthesize the same proteins, breath the same air, etc. Hence, if we learn of hemoglobin actually works for one mammal, we have learned for many more mammals. This seems to happen also for neutron stars so that although there are many equations of state that predict different results for M_max, they all show there is a universal relation between M_max and M_TOV. More specifically, we have found that M_max = 1.203 +- 0.022 M_TOV.”

These findings are likely to have interesting implications when it comes to future astronomical research. For starters, knowing the maximum mass a neutron star can achieve will be useful when analyzing the gravitational-wave signals produced by neutron stars, allowing astronomers to extract information on the equation of state before the object collapses into a black hole.

Second, it will be useful in determining the moment of inertia for neutron stars, i.e. knowing how much mass is required before it begins to rotate. In short, scientists will be able to know with greater accuracy what it takes to set a neutron star to spinning and will able to predict with greater accuracy when a spinning neutron star will be on the verge of collapsing, and thus knowing when and where a new black hole will be.

Al this, in turn, is likely to be a boon for research into black holes, the one object in the universe that is arguably more awe-inspiring and less understood than neutron stars. One step closer to understanding this grand, mysterious thing known as the Universe!

Further Reading: phys.org

 

 

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Ten Interesting Facts About Jupiter

Jupiter's Red Spot, seen by Voyager 1. Image credit: NASA/JPL

Jupiter was appropriately named after the king of the gods. It’s massive, has a powerful magnetic field, and more moons that any planet in the Solar System. Though it has been known to astronomers since ancient times, the invention of the telescope and the advent of modern astronomy has taught us so much about this gas giant.

In short, there are countless interesting facts about this gas giant that many people just don’t know about. And we here at Universe Today have taken the liberty of compiling a list of ten particularly interesting ones that we think will fascinate and surprise you. Think you know everything about Jupiter? Think again!

1. Jupiter Is Massive:

It’s no secret that Jupiter is the largest planet in the Solar System. But this description really doesn’t do it justice. For one, the mass of Jupiter is 318 times as massive as the Earth. In fact, Jupiter is 2.5 times more massive than all of the other planets in the Solar System combined. But here’s the really interesting thing…

If Jupiter got any more massive, it would actually get smaller. Additional mass would actually make the planet more dense, which would cause it to start pulling it in on itself. Astronomers estimate that Jupiter could end up with 4 times its current mass, and still remain about the same size.

2. Jupiter Cannot Become A Star:

Astronomers call Jupiter a failed star, but that’s not really an appropriate description. While it is true that, like a star, Jupiter is rich in hydrogen and helium, Jupiter does not have nearly enough mass to trigger a fusion reaction in its core. This is how stars generate energy, by fusing hydrogen atoms together under extreme heat and pressure to create helium, releasing light and heat in the process.

This is made possible by their enormous gravity. For Jupiter to ignite a nuclear fusion process and become a star, it would need more than 70 times its current mass. If you could crash dozens of Jupiters together, you might have a chance to make a new star. But in the meantime, Jupiter shall remain a large gas giant with no hopes of becoming a star. Sorry, Jupiter!

https://youtu.be/v9HtCAHv54E

3. Jupiter Is The Fastest Spinning Planet In The Solar System:

For all its size and mass, Jupiter sure moves quickly. In fact, with an rotational velocity of 12.6 km/s (~7.45 m/s) or 45,300 km/h (28,148 mph), the planet only takes about 10 hours to complete a full rotation on its axis. And because it’s spinning so rapidly, the planet has flattened out at the poles a little and is bulging at its equator.

In fact, points on Jupiter’s equator are more than 4,600 km further from the center than the poles. Or to put it another way, the planet’s polar radius measures to 66,854 ± 10 km (or 10.517 that of Earth’s), while its diameter at the equator is 71,492 ± 4 km (or 11.209 that of Earth’s). This rapid rotation also helps generate Jupiter’s powerful magnetic fields, and contribute to the dangerous radiation surrounding it.

4. The Clouds On Jupiter Are Only 50 km Thick:

That’s right, all those beautiful whirling clouds and storms you see on Jupiter are only about 50 km thick. They’re made of ammonia crystals broken up into two different cloud decks. The darker material is thought to be compounds brought up from deeper inside Jupiter, and then change color when they reacted with sunlight. But below those clouds, it’s just hydrogen and helium, all the way down.

5. The Great Red Spot has been around for a long time

The Great Red Spot on Jupiter is one of its most familiar features. This persistent anticyclonic storm, which is located south of its equator, measures between 24,000 km in diameter and 12–14,000 km in height. As such, it is large enough to contain two or three planets the size of Earth’s diameter. And the spot has been around for at least 350 years, since it was spotted as far back as the 17th century.

The Great Red Spot was first identified in 1665 by Italian astronomer Giovanni Cassini. By the 20th century, astronomers began to theorize that it was a storm, one which was created by Jupiter’s turbulent and fast-moving atmosphere. These theories were confirmed by the Voyager 1 mission, which observed the Giant Red Spot up close in March of 1979 during its flyby of the planet.

However, it appears to have been shrinking since that time. Based on Cassini’s observations, the size was estimated to be 40,000 km in the 17th century, which was almost twice as large as it is now. Astronomers do not know if or when it will ever disappear entirely, but they are relatively sure that another one will emerge somewhere else on the planet.

6. Jupiter Has Rings:

When people think of ring systems, Saturn naturally comes to mind. But in truth, both Uranus and Jupiter have ring systems of their own. Jupiter’s were the third set to be discovered (after the other two), due to the fact that they are particularly faint. Jupiter’s rings consist of three main segments – an inner torus of particles known as the halo, a relatively bright main ring, and an outer gossamer ring.

These rings are widely believed to have come from material ejected by its moons when they’re struck by meteorite impacts. In particular, the main ring is thought to be composed of material from the moons of Adrastea and Metis, while the moons of Thebe and Amalthea are believed to produce the two distinct components of the dusty gossamer ring.

This material fell into orbit around Jupiter (instead of falling back to their respective moons) because if Jupiter’s strong gravitational influence. The ring is also depleted and replenished regularly as some material veers towards Jupiter while new material is added by additional impacts.

7. Jupiter’s Magnetic Field Is 14 Times Stronger Than Earth’s:

Compasses would really work on Jupiter. That’s because it has the strongest magnetic field in the Solar System. Astronomers think the magnetic field is generated by the eddy currents – i.e. swirling movements of conducting materials – within the liquid metallic hydrogen core. This magnetic field traps particles of sulfur dioxide from Io’s volcanic eruptions, which producing sulfur and oxygen ions. Together with hydrogen ions originating from the atmosphere of Jupiter, these form a plasma sheet in Jupiter’s equatorial plane.

Farther out, the interaction of the magnetosphere with the solar wind generates a bow shock, a dangerous belt of radiation that can cause damage tos spacecraft. Jupiter’s four largest moons all orbit within the magnetosphere, which protects them from the solar wind, but also make the likelihood of establishing outposts on their surface problematic. The magnetosphere of Jupiter is also responsible for intense episodes of radio emission from the planet’s polar regions.

8. Jupiter Has 63 Moons:

As of the penning of this article, Jupiter has a 67 confirmed and named satellites. However, it is estimated that the planet has over 200 natural satellites orbiting it. Almost all of them are less than 10 kilometers in diameter, and were only discovered after 1975, when the first spacecraft (Pioneer 10) arrived at Jupiter.

However, it also has four major moons, which are collectively known as the Galilean Moons (after their discovered Galileo Galilei). These are, in order of distance from Jupiter, Io, Europa, Ganymede, and Callisto. These moons are some of the largest in the Solar System, with Ganymede being the largest, measuring 5262 km in diameter.

9. Jupiter Has Been Visited 7 Times By Spacecraft:

Jupiter was first visited by NASA’s Pioneer 10 spacecraft in December 1973, and then Pioneer 11 in December 1974. Then came the Voyager 1 and 2 flybys, both of which happened in 1979. This was followed by a long break until Ulysses arrived in February 1992. Then Cassini made a flyby in 2000, on its way to Saturn. And finally, NASA’s New Horizons spacecraft made its flyby in 2007. This was the last mission to fly past Jupiter, but it surely won’t be the last.

10. You Can See Jupiter With Your Own Eyes:

Jupiter is the third brightest object in the Solar System, after Venus and the Moon. Chances are, you saw Jupiter in the sky, and had no idea that’s what you were seeing. And here at Universe Today, we are in the habit of letting readers know when the best opportunities for spotting Jupiter in the night sky are.

Chances are, if you see a really bright star high in the sky, then you’re looking at Jupiter. Get your hands on a pair of binoculars, and if you know someone with a telescope, that’s even better. Using even modest magnification, you might even spot small specks of light orbiting it, which are its Galilean Moons. Just think, you’ll be seeing precisely what Galileo did when he gazed at the planet in 1610.

We have written many interesting articles about Jupiter here at Universe Today. Here’s The Gas Giant Jupiter, How Strong Is Jupiter’s Gravity?, Does Jupiter Have A Solid Core?, and Jupiter Compared To Earth.

And here are 10 Interesting Facts About Planet Earth, and 1o Interesting Facts About Mars.

For more information, check out the Hubblesite’s News Releases about Jupiter, and NASA’s Solar System Exploration.

We’ve also recorded an entire show just on Jupiter for Astronomy Cast. Listen to it here, Episode 56: Jupiter, and Episode 57: Jupiter’s Moons.

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Weekly Space Hangout – Mar. 25, 2016: Andrew Helton & Ryan Hamilton of SOFIA

Host: Fraser Cain (@fcain) Guests:This week, we welcome Andrew Helton and Ryan Hamilton, member of the SOFIA Telescope Team. Andrew is the Instrument Scientist for the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST) dual channel, mid-infrared camera and spectrograph, one of the observatory’s facility-class science instruments. Ryan is the Instrument Scientist for the […]

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What Does It Mean To Be ‘Star Stuff’?

At one time or another, all science enthusiasts have heard the late Carl Sagan’s infamous words: “We are made of star stuff.” But what does that mean exactly? How could colossal balls of plasma, greedily burning away their nuclear fuel in faraway time and space, play any part in spawning the vast complexity of our Earthly world? How is it that “the nitrogen in […]

Possible Bright Supernova Lights Up Spiral Galaxy M61

I sat straight up in my seat when I learned of the discovery of a possible new supernova in the bright Virgo galaxy M61. Since bright usually means close, this newly exploding star may soon become visible in smaller telescopes. It was discovered at magnitude +13.6 on October 29th by Koichi Itagaki of Japan who holds […]