Tag: Star

NASA’s New Planet Hunter Has Already Spotted Two Candidates For Earth-Like Alien Worlds

 

NASA’s Transiting Exoplanet Survey Satellite (TESS) has only been on the job less than two months, and already it’s ponying up the planet goods.

The exoplanet-hunting space telescope has found two candidate planets, and there are plenty more on the horizon.

The two candidate planets are called Pi Mensae c, orbiting bright yellow dwarf star Pi Mensae, just under 60 light-years from Earth; and LHS 3844 b, orbiting red dwarf star LHS 3844, just under 49 light-years away.

TESS took its first test observations on July 25 (and managed to get some pretty great snaps of a passing comet), and its first official science observations began on August 7.

However, it was observing a large swathe of sky from the moment it opened its eyes – four optical cameras – and both discoveries are based on data from July 25 to August 22.

So far, they are only candidate planets, yet to be validated by the final review process. If they pass that test, they’ll go down in history as TESS’s first two discoveries. Here’s what we know so far about them.

Both planets appear to be Earth-like and rocky, but neither is habitable according to our guidelines – both are too close to their stars for liquid water.

Pi Mensae c, the first planet announced, is a super-Earth, clocking in at just over twice the size of Earth. It’s really close to Pi Mensae – it orbits the star in just 6.27 days.




A preliminary analysis indicates that the planet has a rocky iron core, and also contains a substantial proportion of lighter materials such as water, methane, hydrogen and helium – although we’ll need a more detailed survey to confirm that.

It also has a sibling – it’s not the first object to be found orbiting Pi Mensae. That honour goes to Pi Mensae b, an enormous planet with 10 times the mass of Jupiter discovered in 2001.

It’s much farther out than Pi Mensae c, on an orbit of 2,083 days. LHS 3844 b is a little bit smaller, classified as a “hot Earth“.

It’s just over 1.3 times the size of Earth, and on an incredibly tight orbit of just 11 hours. Since the two are so close together, it’s highly likely the planet is blasted with too much stellar radiation to retain an atmosphere.

TESS does need a bit of time to collect enough data for identifying an exoplanet.

Like its predecessor Kepler, it uses what is known as the transit method for detection – scanning and photographing a region of the sky multiple times, looking for changes in the brightness of stars in its field of view.

When a star dims repeatedly and regularly, that is a good indication that a planet is passing between it and TESS.

By using the amount the light dims, and Doppler spectroscopy – that is, changes in the star’s light as it moves ever-so-slightly backwards and forwards due to the gravitational tug on the planet – astronomers can infer details about the planet, such as its size and mass.

 

Using this method, Kepler has discovered 2,652 confirmed planets to date between its first and second missions, located between 300 to 3,000 light-years away.

Kepler is still operational, but barely; it’s only a matter of time until it completely runs out of fuel.

TESS’s search is happening a lot closer, with targets between 30 and 300 light-years away – stars brighter than those observed by Kepler.

Thus, the exoplanets it identifies will be strong candidates to observe using spectroscopy, the analysis of light.

When a planet passes in front of a star, it has an effect on the light from the star, changing it based on the composition of its atmosphere (if it has one).

Ground-based observatories and the James Webb Space Telescope (once it launches in 2021) will have to make those follow-up observations.

Both papers are available on preprint resource arXiv. Pi Mensa c can be found here, and LHS 3844 b can be found here.

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Pass it on: Popular Science

 

Atomic Iron And Titanium In The Atmosphere Of The Exoplanet KELT-9b

To constrain the formation history of an exoplanet, we need to know its chemical composition.

With an equilibrium temperature of about 4,050 kelvin, the exoplanet KELT-9b (also known as HD 195689b) is an archetype of the class of ultrahot Jupiters that straddle the transition between stars and gas-giant exoplanets and are therefore useful for studying atmospheric chemistry.

At these high temperatures, iron and several other transition metals are not sequestered in molecules or cloud particles and exist solely in their atomic forms




However, despite being the most abundant transition metal in nature, iron has not hitherto been detected directly in an exoplanet because it is highly refractory.

The high temperatures of KELT-9b imply that its atmosphere is a tightly constrained chemical system that is expected to be nearly in chemical equilibrium and cloud-free, and it has been predicted that spectral lines of iron should be detectable in the visible range of wavelengths.

Here we report observations of neutral and singly ionized atomic iron (Fe and Fe+) and singly ionized atomic titanium (Ti+) in the atmosphere of KELT-9b.

We identify these species using cross-correlation analysis of high-resolution spectra obtained as the exoplanet passed in front of its host star.

Similar detections of metals in other ultrahot Jupiters will provide constraints for planetary formation theories.

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Pass it on: Popular Science

A New Study Suggests That As A Star Begins To Die And Slowly Expands Outward, It Would Temporarily Light Up As It Eats The Worlds It Hosts

600 light years away, in the constellation of Auriga, there is a star in some ways similar to our Sun. It’s a shade hotter (by about 800° C), more massive, and older.

Oddly, it appears to be laced with heavy elements: more oxygen, aluminum, and so on, than might be expected. A puzzle.

Then, last year, it was discovered that this star had a planet orbiting it. A project called WASP – Wide Area Search for Planets, a UK telescope system that searches for exoplanets — noticed that the star underwent periodic dips in its light.

This indicates that a planet circles the star, and when the planet gets between the star and us, it blocks a tiny fraction of the starlight.




The planet is a weirdo, for many reasons… but it won’t be weird for too much longer. That’s because the star is eating it.

OK, first, the planet. Called WASP 12b, it was instantly pegged as an oddball. The orbit is only 1.1 days long! Compare that to our own 365 day orbit, or even Mercury’s 88 days to circle the Sun.

This incredibly short orbital period means this planet is practically touching the surface of its star as it sweeps around at over 220 km/sec!

That also means it must be very hot; models indicate that the temperature at its cloud tops would be in excess of 2200°C.

Not only that, but other numbers were odd, too. WASP 12b was found to be a bit more massive and bigger than Jupiter; about 1.8 times its size and 1.4 times its mass.

That’s too big! Models indicate that planets this massive have a funny state of matter in them; they are so compressible that if you add mass, the planet doesn’t really get bigger, it just gets denser.

In other words, you could double Jupiter’s mass and its size wouldn’t increase appreciably, but since the mass goes up, so would its density.

But WASP 12b isn’t like that. In fact, it has a lower density than Jupiter, and is a lot bigger! Something must be going on… and when you see a lot of weird things all sitting in one place, it makes sense to assume they’re connected.

In this case it’s true: that planet is freaking hot, and that’s at the heart of this mess. Heating a planet that much would not exactly be conducive to its well-being.

When you heat a gas it expands, which would explain WASP 12b’s big size. It’s puffy! But being all bloated that close to a star turns out to be bad for your health.

Astronomers used Hubble to observe the planet in the ultraviolet and found clear signs of all sorts of heavy elements, including sodium, tin, aluminum, magnesium, and manganese, as well as, weirdly, ytterbium*.

Moreover, they could tell from the data that these elements existed in a cloud surrounding the planet, like an extended atmosphere going outward for hundreds of thousands of kilometers.

This explains the peculiar high abundance of heavy metals in the star I mentioned at the beginning of this post; they come from the planet! But not for long.

Given the mass of the planet and the density of the stream, it looks like it has roughly ten million years left. At that point, supper’s over: there won’t be anything left for the star to eat.

In reality it’s hard to say exactly what will happen; there may be a rocky/metal core to the planet that will survive. But even that is so close to the star that it will be a molten blob of goo.

The way orbits work, the way the dance of gravity plays out over time, the planet itself may actually be drawn inexorably closer to its star. Remember, too, the star is old, and will soon start to expand into a red giant.

So the planet is falling and the star is rising; eventually the two will meet and the planet will meet a fiery death.

All in all, it sucks to be WASP 12b.

But it’s cool to be an astronomer!

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Pass it on: New Scientist

No ‘Alien Megastructure’ Around Tabby’s Star, Only Cosmic Dustbunnies

Sorry to burst your bubble, folks, but the mysteriously dimming Tabby’s Star isn’t due to an “alien megastructure” after all – it’s just obscured by dust, according to a paper published today.

KIC 8462852 (but Tabby’s Star is catchier) was first spotted by NASA’s Kepler telescope.

It quickly became an object of fascination for citizen scientists working for the Planet Hunters project, hoping to discover why its brightness levels weirdly dipped for prolonged periods.

Other than that, it’s a pretty regular flaming gas ball.




Located in the Cygnus constellation, the F-type main sequence star is about 1,000 light years away, and is about 50 per cent bigger and 1,000oC (1,832oF) hotter than the Sun.

Several hypotheses have been suggested for the dimming light. Some people thought it was due to cold comet fragments circling the star in a highly eccentric orbit. Others believed it was a sign of extraterrestrial life trying to communicate.

Over 1,700 people donated more than $107,000 (£73,708) through a Kickstarter campaign to support a team of more than 200 researchers to observe the star at the Las Cumbres Observatory in Goleta, California, from March 2016 to December 2017.

The results have now been published in The Astrophysical Journal and suggest the dimming is all just down to, er, dust. NASA also proposed dust in uneven rings as the cause back in October last year.

Jason Wright, co-author of the paper and an astrophysics assistant professor at Pennsylvania State University, said: “We were hoping that once we finally caught a dip happening in real time we could see if the dips were the same depth at all wavelengths.

If they were nearly the same, this would suggest that the cause was something opaque, like an orbiting disk, planet, or star, or even large structures in space.

But careful analysis showed that the intensity of the dimming of the light varied across different wavelengths.

Tabetha Boyajian, lead author of the study and an assistant professor of astrophysics at Louisiana State University, said: “Dust is most likely the reason why the star’s light appears to dim and brighten.

The new data shows that different colors of light are being blocked at different intensities. Therefore, whatever is passing between us and the star is not opaque, as would be expected from a planet or alien megastructure.”

Although the results rule out more exotic explanations, they still raises interesting questions, Wright said.

Boyajian said the prospect was “exciting”.

I am so appreciative of all of the people who have contributed to this in the past year – the citizen scientists and professional astronomers.

“It’s quite humbling to have all of these people contributing in various ways to help figure it out.

“If it wasn’t for people with an unbiased look on our universe, this unusual star would have been overlooked.”

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Pass it on: New Scientist

Could Our Milky Way’s Many Brown And White Dwarf Stars Be Home To Alien Life?

The dead and failed stars known as white dwarfs and brown dwarfs can give off heat that can warm up worlds, but their cooling natures and harsh light make them unlikely to host life, researchers say.

Stars generally burn hydrogen to give off light and heat up nearby worlds.

However, there are other bodies in space that can shine light as well, such as the failed stars known as brown dwarfs and the dead stars known as white dwarfs.

White dwarfs are remnants of normal stars that have burned all the hydrogen in their cores. Still, they can remain hot enough to warm nearby planets for billions of years.

Planets around white dwarfs might include the rocky cores of worlds that were in orbit before the star that became the white dwarf perished; new planets might also emerge from envelopes of gas and dust around white dwarfs.

Brown dwarfs are gaseous bodies that are larger than the heaviest planets but smaller than the lightest stars.




This means they are too low in mass for their cores to squeeze hydrogen with enough pressure to support nuclear fusion like regular stars.

Still, the gravitational energy from their contractions does get converted to heat, meaning they can warm their surroundings.

NASA’s WISE spacecraft and other telescopes have recently discovered hundreds of brown dwarfs, raising the possibility of detecting exoplanets circling them; scientists have already observed protoplanetary disks around a few of them.

White dwarfs and brown dwarfs are bright enough to support habitable zones — regions around them warm enough for planets to sustain liquid water on their surfaces.

As such, worlds orbiting them might be able support alien life as we know it, as there is life virtually everywhere there is water on Earth.

An added benefit of looking for exoplanets around these dwarfs is that they might be easier to detect than ones around regular stars.

These dwarfs are relatively small and faint, meaning any worlds that pass in front of them would dim them more noticeably than planets crossing in front of normal stars.

However, unlike regular stars, white dwarfs and brown dwarfs cool as they age, meaning their habitable zones will move inward over time.

The most obvious peril of a shifting habitable zone is that it could result in a planet getting so cold all the liquid water on its surface freezes solid.

There are other dangers, however — as white dwarfs and brown dwarfs cool, the light they give off would change as well, possibly meaning they would end up sterilizing worlds with dangerous, high-energy radiation.

To be specific, extreme ultraviolet rays would break a planet’s water apart into hydrogen and oxygen. The hydrogen can escape into space, and without hydrogen to bond with oxygen, the world has no water and is not habitable.

Such exoplanets would resemble Venus, with dry atmospheres dominated by carbon dioxide.

In addition, because white dwarfs and brown dwarfs are so dim, their habitable zones already start off very near them.

About one-hundredth the distance between the sun and Earth, which is about one-thirtieth the distance between the sun and Mercury.

White dwarfs should tidally heat planets more than brown dwarfs, since white dwarfs are so massive, the researchers noted.

White dwarfs are only about the size of the Earth, but they are remarkably dense, with masses nearly two-thirds that of the sun.

All in all, the scientists found it unlikely that planets orbiting white dwarfs would ever be truly habitable.

When they are young, white dwarfs would blast planets in their habitable zones with ultraviolet rays that would strip the worlds of water.

When they grow older, their habitable zones would shift closer to them, and the amount of tidal heating might also end up desiccating any planets residing in those zones.

Although the chances for life around white dwarfs and brown dwarfs might look slim, they are not zero, the scientists cautioned.

For instance, a planet might drift into the habitable zone of a white dwarf from a more distant orbit long after the formation of that dead star.

It would still have to contend with tidal heating, but it would have avoided radiation that likely would have sterilized its surface.

More research is needed to understand how planets orbiting white dwarfs and brown dwarfs form, and “particularly the amount of water they form with,” Barnes said,  a planetary scientist and astrobiologist at the University of Washington at Seattle

We also need to understand how the high-energy radiation of brown dwarfs evolves with time. This is the energy that can remove water, but we don’t have any idea how strong it can be, and how long it lasts.”

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Pass it on: New Scientist

It Was A Universe-Shaking Announcement. But What Is A Neutron Star Anyway?

Last October 16, 2017, astronomers made a universe-shaking announcement about the detection of reverberations from the collision of two neutron stars.

It is another triumph for LIGO, short for Laser Interferometer Gravitational-Wave Observatory, the instrument that has opened a new window into the universe by detecting shakings in the fabric of space-time known as gravitational waves.

Previously, LIGO, had detected three mergers of black holes. Scientists who helped create LIGO also just won the Nobel Prize in Physics.

The new discovery sheds light on a smaller, different type of rumbling, one that can be both seen and heard. Here are answers to some questions you might have about the discovery.




What’s a neutron star?

Let’s back up a step: what’s a neutron? An atom consists of a heavy center known as the nucleus, surrounded by a cloud of tiny negatively charged electrons.

In the nucleus are two types of particles: positively charged protons and electrically neutral neutrons.

A neutron star, as its name suggests, is a star that consists almost entirely of neutrons.

Here’s how that neutron star formed:

For most of their existence, stars emit light through fusion the merging of hydrogen atoms into helium, which releases gargantuan amounts of energy.

When a large star probably at least six times the mass of the sun exhausts its hydrogen, it begins to collapse.

The collapse accelerates so quickly that it sets off cataclysmic explosion known as a supernova. What’s left over is an extremely dense cinder that is only about six miles wide, but packs in more mass than the sun.

The pressure is so great that electrons and protons are squeezed together into neutrons.

A single thimbleful of a neutron star weighs as much as several million elephants.

How does a neutron star differ from a black hole?

A neutron star is a stellar cinder that stopped collapsing.

But when even larger stars explode, the remaining core is so dense that the core continues collapsing until it turns into a black hole. Here’s our guide to black holes.

What happens when two neutron stars collide?

In the case of the discovery that was detailed last October 16, 2017, the merging objects were probably survivors of massive stars that had been orbiting each other and had each puffed up and then died in spectacular supernova explosions.

Making reasonable assumptions about their spins, the astronomers calculated that these neutron stars were about 1.1 and 1.6 times as massive as the sun, smack in the known range of neutron stars.

As they approached each other, swirling a thousand times a second, tidal forces bulged their surfaces outward. Quite a bit of the material was ejected and formed a fat doughnut around the merging stars.

At the moment they touched each other, a shock wave squeezed more material out of their polar regions, but the doughnut and extreme magnetic fields confined the material into an ultra-high-speed jet emitting a blitzkrieg of radiation.

That blast set off the gravitational waves detected by LIGO, as well as the light show spotted by a variety of telescopes.

What are gravitational waves?

Watch this video we made in 2016 when LIGO first detected them to learn more about these ripples in space-time that confirmed key aspects of Albert Einstein’s theories.

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Pass it on: New Scientist

Mystery Of The Zombie Star That Won’t Die

A brightly burning ‘zombie‘ supernova that refuses to die has left astronomers baffled.

The star, which lies half a billion light years away, has exploded numerous times since 1954.

This has stumped astronomers as supernovas are generally considered to explode just once and standard theoretical models cannot explain its behaviour.

Researchers at Las Cumbres Observatory in Goleta, California, have been studying the phenomenon, which was first observed in 2014 by the Intermediate Palomar Transient Factory telescope near San Diego.

In January 2015 the event, known as iPTF14hls, was classified as a type II-P supernova, which results from the rapid collapse and violent explosion of a single massive star.




This type of supernova gives off a distinctive flash and tend to stay bright for around 100 days and supernovae lasting more than 130 days are extremely rare.

But iPTF14hls remained bright for almost two years (600 days), with the brightness of the light it emitted varying by up to 50 per cent over this time, as if it were exploding over and over again.

The evolution of the event also seems to be taking place roughly ten times slower than others of its type.

Adding to the puzzle, telescope imagery uncovered by the team suggests explosions may have taken place at the same location in 1954.

Supernovae are known to explode only once, shine for a few months and then fade, but iPTF14hls experienced at least two explosions, 60 years apart.

Writing in an opinion piece for the journal Nature, Stan Woosley, a professor of astronomy at the University of California, Santa Cruz, said of the findings.

As of now, no detailed model has been published that can explain the observed emission and constant temperature of iPTF14hls, let alone the possible eruption 60 years before the supernova.

“A better understanding could provide insight into the evolution of the most massive stars, the production of the brightest supernovae and possibly the birth of black holes that have masses near 40 solar masses, such as those associated with the first direct detection of gravitational waves.”

“For now, the supernova offers astronomers their greatest thrill: something they do not understand.”

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Pass it on: New Scientist

Scientists Catch A White Dwarf Star In The Act Of Exploding Into A Nova

It’s not every day you get to see a star go nova. Scientists at Warsaw University Observatory in Poland have managed to catch a binary star system both before and after its explosive flash.

The findings, described in the journal Nature, confirm a long-held theory about novae known as the hibernation hypothesis – and could potentially help scientists better understand when such stellar outbursts occur.

Novae are typically caused by a gravitationally locked pair of stars, called a binary system, consisting of one white dwarf and a companion star.




A white dwarf is an aging star that has already shed much of its mass, leaving behind a small but massive core.

Like a gravitational vampire, the white dwarf siphons off material from its stellar companion – and every so often, the system becomes so unstable that the white dwarf erupts, producing a cataclysmic explosion that causes it to flare brightly in the night sky.

The most spectacular eruptions, with a ten-thousandfold increase in brightness, occur in classical novae and are caused by a thermonuclear runaway on the surface of the white dwarf,” the study authors wrote.

Such eruptions are thought to recur on time scales of ten thousand to a million years.”

Such explosions might actually have seeded the universe with some elements and radioactive isotopes, such as lithium, said lead author Przemek Mroz, an astronomer at the observatory.

About 50 novae go off every year in the Milky Way, but only five to 10 are actually observed because most of them are shrouded by interstellar gas and dust, Mroz said in an email.

The closest and brightest, however, can potentially be picked out with the naked eye.

But though novae can be seen once they go off, scientists don’t often get the chance to study them in depth before they explode.

Researchers have long had a theory about the cycle that causes these novae: When the mass transfer is low, the accretion grows unstable; every so often, the white dwarf experiences what the authors called “dwarf nova outbursts.”

Dwarf nova outbursts occur when material from the accretion disk is dumped onto the star’s surface, Mroz said; the dramatic classical nova event occurs on the surface of the white dwarf when there is enough gas to ignite thermonuclear reactions.

This is the first time [that] we observed a dwarf nova that transformed into a classical nova,” Mroz said of his team’s findings.

When the classical nova explosion finally occurs, it actually boosts the mass-transfer rate for centuries, keeping the system more stable until it dwindles and begins to approach the “hibernation” period, thus repeating the process.

But scientists couldn’t say what was really happening until the nova V1213 Cen flashed in 2009 and was caught by the university’s Optical Gravitational Lensing Experiment.

“This discovery would be impossible without long-term observations by the OGLE survey,” Mroz wrote in an email.

The survey started almost 25 years ago and for 20 years we have had a dedicated 1.3-meter telescope at Las Campanas Observatory in Chile. This is another case when OGLE data are crucial for studying unique, extremely rare phenomena.

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Pass it on: New Scientist