Important Science Info Guys.

(by lorenz.weisse)

Visual representation of how the Solar System travels through the Milky Way

via reddit

What are brown dwarfs?

In order to understand what is a brown dwarf, we need to understand the difference between a star and a planet. It is not easy to tell a star from a planet when you look up at the night sky with your eyes. However, the two kinds of objects look very different to an astronomer using a telescope or spectroscope. Planets shine by reflected light; stars shine by producing their own light. So what makes some objects shine by themselves and other objects only reflect the light of some other body? That is the important difference to understand – and it will allow us to understand brown dwarfs as well.

As a star forms from a cloud of contracting gas, the temperature in its center becomes so large that hydrogen begins to fuse into helium – releasing an enormous amount of energy which causes the star to begin shining under its own power. A planet forms from small particles of dust left over from the formation of a star. These particles collide and stick together. There is never enough temperature to cause particles to fuse and release energy. In other words, a planet is not hot enough or heavy enough to produce its own light.

Brown dwarfs are objects which have a size between that of a giant planet like Jupiter and that of a small star. In fact, most astronomers would classify any object with between 13 times the mass of Jupiter and 75 times the mass of Jupiter to be a brown dwarf. Given that range of masses, the object would not have been able to sustain the fusion of hydrogen like a regular star; thus, many scientists have dubbed brown dwarfs as “failed stars”.

A Trio of Brown Dwarfs

This artist’s conception illustrates what brown dwarfs of different types might look like to a hypothetical interstellar traveler who has flown a spaceship to each one. Brown dwarfs are like stars, but they aren’t massive enough to fuse atoms steadily and shine with starlight – as our sun does so well.

On the left is an L dwarf, in the middle is a T dwarf, and on the right is a Y dwarf. The objects are progressively cooler in atmospheric temperatures as you move from left to right. Y dwarfs are the newest and coldest class of brown dwarfs and were discovered by NASA’s Wide-field Infrared Survey Explorer, or WISE. WISE was able to detect these Y dwarfs for the first time because it surveyed the entire sky deeply at the infrared wavelengths at which these bodies emit most of their light. The L dwarf is seen as a dim red orb to the eye. The T dwarf is even fainter and appears with a darker reddish, or magenta, hue. The Y dwarf is dimmer still. Because astronomers have not yet detected Y dwarfs at the visible wavelengths we see with our eyes, the choice of a purple hue is done mainly for artistic reasons. The Y dwarf is also illustrated as reflecting a faint amount of visible starlight from interstellar space.

In this rendering, the traveler’s spaceship is the same distance from each object. This illustrates an unusual property of brown dwarfs – that they all have the same dimensions, roughly the size of the planet Jupiter, regardless of their mass. This mass disparity can be as large as fifteen times or more when comparing an L to a Y dwarf, despite the fact that both objects have the same radius. The three brown dwarfs also have very different atmospheric temperatures. A typical L dwarf has a temperature of 2,600 degrees Fahrenheit (1,400 degrees Celsius). A typical T dwarf has a temperature of 1,700 degrees Fahrenheit (900 degrees Celsius). The coldest Y dwarf so far identified by WISE has a temperature of less than about 80 degrees Fahrenheit (25 degrees Celsius).

Sources: starchild.gsfc.nasa.gov & nasa.gov 

 image credit: NASA / JPL-Caltech

In Roman mythology, the god Jupiter drew a veil of clouds around himself to hide his mischief. It was only Jupiter’s wife, the goddess Juno, who could peer through the clouds and reveal Jupiter’s true nature. ⁣ ⁣ Our @NASAJuno spacecraft is looking beneath the clouds of the massive gas giant, not seeking signs of misbehavior, but helping us to understand the planet’s structure and history…⁣ ⁣ Now, @NASAJuno just published its first findings on the amount of water in the gas giant’s atmosphere. The Juno results estimate that at the equator, water makes up about 0.25% of the molecules in Jupiter’s atmosphere — almost three times that of the Sun. An accurate total estimate of this water is critical to solving the mystery of how our solar system formed. 

The JunoCam imager aboard Juno captured this image of Jupiter’s southern equatorial region on Sept. 1, 2017. The bottom image is oriented so Jupiter’s poles (not visible) run left-to-right of frame.

Image credit: NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill ⁣ ⁣

It makes me sad how no one ever seems to mention how wild the crocodilian-line archosaurs were. Dinosaurs get all the attention when there was equally crazy shit happening on the other branch of the archosaur tree.

There was a whole linage of bipedal crocodylomorphs during the Triassic that were basically identical to theropod dinosaurs, so much so that a lot of them were initially classified as dinosaurs!

Just fucking look at them!

And these weren’t just little lizard guys, there were some big lads running around.

Not to mention the long-legged ones that galloped around on all fours like some kind of terrifying reptilian dogs.

These crazy crocodiles aren’t just from the Triassic, either; there was a galloping, hoofed crocodilian that lived during the Eocene and likely hunted horses. (They were smaller and not quite as fast as modern horses, but still)

But don’t worry, they weren’t all meat-eaters! There were vegetarian and omnivore crocodylomorphs too! Just look at this guy!

He was an ankylosaur before ankylosaurs were cool (or even existed).

Captain’s Log | September 15, 2017

The end is now upon us. Within hours of the posting of this entry, Cassini will have burned up in the atmosphere of Saturn … a kiloton explosion, spread out against the sky in a pyrrhic display of light and fire, a dazzling flash to signal the dying essence of a lone emissary from another world. As if the myths of old had foretold the future, the great patriarch will consume his child. At that point, that golden machine, so dutiful and strong, will enter the realm of history, and the toils and triumphs of this long march will be done.

For those of us appointed long ago to undertake this journey, it has been a taxing 3 decades, requiring a level of dedication that I could not have predicted, and breathless times when we sprinted for the duration of a marathon. But in return, we were blessed to spend our lives working and playing in that promised land beyond the Sun.

My imaging team members and I were especially blessed to serve as the documentarians of this historic epoch and return a stirring visual record of our travels around Saturn and the glories that we found there. This is our gift to the citizens of planet Earth.

So, it is with both wistful, sentimental reflection and a boundless sense of pride in a commitment met and a job well done that I now turn to face this looming, abrupt finality.

It is doubtful we will soon see a mission as richly suited as Cassini return to this ringed world and shoulder a task as colossal as we have borne over the last 27 years.

To have served on this mission has been to live the rewarding life of an explorer of our time, a surveyor of distant worlds. We wrote our names across the sky. We could not have asked for more.

I sign off now, grateful in knowing that Cassini’s legacy, and ours, will include our mutual roles as authors of a tale that humanity will tell for a very long time to come.

The Stellar Buddy System

Our Sun has an entourage of planets, moons, and smaller objects to keep it company as it traverses the galaxy. But it’s still lonely compared to many of the other stars out there, which often come in pairs. These cosmic couples, called binary stars, are very important in astronomy because they can easily reveal things that are much harder to learn from stars that are on their own. And some of them could even host habitable planets!

The birth of a stellar duo

New stars emerge from swirling clouds of gas and dust that are peppered throughout the galaxy. Scientists still aren’t sure about all the details, but turbulence deep within these clouds may give rise to knots that are denser than their surroundings. The knots have stronger gravity, so they can pull in more material and the cloud may begin to collapse.

The material at the center heats up. Known as a protostar, it is this hot core that will one day become a star. Sometimes these spinning clouds of collapsing gas and dust may break up into two, three, or even more blobs that eventually become stars. That would explain why the majority of the stars in the Milky Way are born with at least one sibling.

Seeing stars

We can’t always tell if we’re looking at binary stars using just our eyes. They’re often so close together in the sky that we see them as a single star. For example, Sirius, the brightest star we can see at night, is actually a binary system (see if you can spot both stars in the photo above). But no one knew that until the 1800s.

Precise observations showed that Sirius was swaying back and forth like it was at a middle school dance. In 1862, astronomer Alvan Graham Clark used a telescope to see that Sirius is actually two stars that orbit each other.

But even through our most powerful telescopes, some binary systems still masquerade as a single star. Fortunately there are a couple of tricks we can use to spot these pairs too.

Since binary stars orbit each other, there’s a chance that we’ll see some stars moving toward and away from us as they go around each other. We just need to have an edge-on view of their orbits. Astronomers can detect this movement because it changes the color of the star’s light – a phenomenon known as the Doppler effect.

Stars we can find this way are called spectroscopic binaries because we have to look at their spectra, which are basically charts or graphs that show the intensity of light being emitted over a range of energies. We can spot these star pairs because light travels in waves. When a star moves toward us, the waves of its light arrive closer together, which makes its light bluer. When a star moves away, the waves are lengthened, reddening its light.

Sometimes we can see binary stars when one of the stars moves in front of the other. Astronomers find these systems, called eclipsing binaries, by measuring the amount of light coming from stars over time. We receive less light than usual when the stars pass in front of each other, because the one in front will block some of the farther star’s light.

Sibling rivalry

Twin stars don’t always get along with each other – their relationship may be explosive! Type Ia supernovae happen in some binary systems in which a white dwarf – the small, hot core left over when a Sun-like star runs out of fuel and ejects its outer layers – is stealing material away from its companion star. This results in a runaway reaction that ultimately detonates the thieving star. The same type of explosion may also happen when two white dwarfs spiral toward each other and collide. Yikes!

Scientists know how to determine how bright these explosions should truly be at their peak, making Type Ia supernovae so-called standard candles. That means astronomers can determine how far away they are by seeing how bright they look from Earth. The farther they are, the dimmer they appear. Astronomers can also look at the wavelengths of light coming from the supernovae to find out how fast the dying stars are moving away from us.

Studying these supernovae led to the discovery that the expansion of the universe is speeding up. Our Nancy Grace Roman Space Telescope will scan the skies for these exploding stars when it launches in the mid-2020s to help us figure out what’s causing the expansion to accelerate – a mystery known as dark energy.

Spilling stellar secrets

Astronomers like finding binary systems because it’s a lot easier to learn more about stars that are in pairs than ones that are on their own. That’s because the stars affect each other in ways we can measure. For example, by paying attention to how the stars orbit each other, we can determine how massive they are. Since heavier stars burn hotter and use up their fuel more quickly than lighter ones, knowing a star’s mass reveals other interesting things too.

By studying how the light changes in eclipsing binaries when the stars cross in front of each other, we can learn even more! We can figure out their sizes, masses, how fast they’re each spinning, how hot they are, and even how far away they are. All of that helps us understand more about the universe.

Tatooine worlds

Thanks to observatories such as our Kepler Space Telescope, we know that worlds like Luke Skywalker’s home planet Tatooine in “Star Wars” exist in real life. And if a planet orbits at the right distance from the two stars, it could even be habitable (and stay that way for a long time).

In 2019, our Transiting Exoplanet Survey Satellite (TESS) found a planet, known as TOI-1338 b, orbiting a pair of stars. These worlds are tricker to find than planets with only one host star, but TESS is expected to find several more!

Want to learn more about the relationships between stellar couples? Check out this Tumblr post: https://nasa.tumblr.com/post/190824389279/cosmic-couples-and-devastating-breakups

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

Lunar Sand taken from the rim of the Shorty Crater by the Apollo 17 Astronauts. This “Orange Soil” is a result of volcanic activity on The Moon 3.8 billion years ago. It is so spherical and smooth due to the lack of gravity - pulling the molten substance in towards itself at the time of eruption and thus creating these round particles. ⠀

⠀Via Gary Greenberg, Carol Kiely, and Kate Clover

“Nightfall”, by Asimov and Silverberg

I haven’t picked a book apart in a while, so have some mildly-disjointed thoughts on Asimov & Silverberg’s 1989 novel, mostly focused on the somewhat-ropey astronomy, but looking at a few other things as well…

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