NASA Science Show & Tell

Will we one day explore the worlds of our solar system? How long will this take?

We have a diversity of worlds in our solar system. Majestic places…

Imagine being able to visit Mars and its hostile climate. Imagine being able to visit the moons of Jupiter, observe Io: the volcanic moon, Europa, the frozen moon and Ganymede a moon larger than Mercury itself and that has its own magnetic field. Imagine visiting the moons of Saturn and maybe passing close to your rings… Imagine orbiting or floating through Titan’s atmosphere and closely watching its lakes and seas of methane and liquid ethane. Imagine getting to know the geysers of Enceladus, the valleys of Tethys, and the craters of Mimas… Imagine being able to see the moons of Uranus and have a view of Verona Rupes, the largest cliff of the solar system, located in Miranda. Imagine being able to be in Triton and to be able to observe the cold and azualdo Neptune in the sky…

Cosmic rays

Cosmic rays provide one of our few direct samples of matter from outside the solar system. They are high energy particles that move through space at nearly the speed of light. Most cosmic rays are atomic nuclei stripped of their atoms with protons (hydrogen nuclei) being the most abundant type but nuclei of elements as heavy as lead have been measured. Within cosmic-rays however we also find other sub-atomic particles like neutrons electrons and neutrinos.

Since cosmic rays are charged – positively charged protons or nuclei, or negatively charged electrons – their paths through space can be deflected by magnetic fields (except for the highest energy cosmic rays). On their journey to Earth, the magnetic fields of the galaxy, the solar system, and the Earth scramble their flight paths so much that we can no longer know exactly where they came from. That means we have to determine where cosmic rays come from by indirect means.

Because cosmic rays carry electric charge, their direction changes as they travel through magnetic fields. By the time the particles reach us, their paths are completely scrambled, as shown by the blue path. We can’t trace them back to their sources. Light travels to us straight from their sources, as shown by the purple path.

One way we learn about cosmic rays is by studying their composition. What are they made of? What fraction are electrons? protons (often referred to as hydrogen nuclei)? helium nuclei? other nuclei from elements on the periodic table? Measuring the quantity of each different element is relatively easy, since the different charges of each nucleus give very different signatures. Harder to measure, but a better fingerprint, is the isotopic composition (nuclei of the same element but with different numbers of neutrons). To tell the isotopes apart involves, in effect, weighing each atomic nucleus that enters the cosmic ray detector.

All of the natural elements in the periodic table are present in cosmic rays. This includes elements lighter than iron, which are produced in stars, and heavier elements that are produced in violent conditions, such as a supernova at the end of a massive star’s life.

Detailed differences in their abundances can tell us about cosmic ray sources and their trip through the galaxy. About 90% of the cosmic ray nuclei are hydrogen (protons), about 9% are helium (alpha particles), and all of the rest of the elements make up only 1%. Even in this one percent there are very rare elements and isotopes. Elements heavier than iron are significantly more rare in the cosmic-ray flux but measuring them yields critical information to understand the source material and acceleration of cosmic rays.

Even if we can’t trace cosmic rays directly to a source, they can still tell us about cosmic objects. Most galactic cosmic rays are probably accelerated in the blast waves of supernova remnants. The remnants of the explosions – expanding clouds of gas and magnetic field – can last for thousands of years, and this is where cosmic rays are accelerated. Bouncing back and forth in the magnetic field of the remnant randomly lets some of the particles gain energy, and become cosmic rays. Eventually they build up enough speed that the remnant can no longer contain them, and they escape into the galaxy.

Cosmic rays accelerated in supernova remnants can only reach a certain maximum energy, which depends on the size of the acceleration region and the magnetic field strength. However, cosmic rays have been observed at much higher energies than supernova remnants can generate, and where these ultra-high-energies come from is an open big question in astronomy. Perhaps they come from outside the galaxy, from active galactic nuclei, quasars or gamma ray bursts.

Or perhaps they’re the signature of some exotic new physics: superstrings, exotic dark matter, strongly-interacting neutrinos, or topological defects in the very structure of the universe. Questions like these tie cosmic-ray astrophysics to basic particle physics and the fundamental nature of the universe. (source)

If the Moon were replaced with some of our planets (at night)

Image credit: yeti dynamics

Blanet: A new class of planet that could form around black holes

The dust clouds around supermassive black holes are the perfect breeding ground for an exotic new type of planet.

Blanets are fundamentally similar to planets; they have enough mass to be rounded by their own gravity, but are not massive enough to start thermonuclear fusion, just like planets that orbit stars. In 2019, a team of astronomers and exoplanetologists showed that there is a safe zone around a supermassive black hole that could harbor thousands of blanets in orbit around it.

The generally agreed theory of planet formation is that it occurs in the protoplanetary disk of gas and dust around young stars. When dust particles collide, they stick together to form larger clumps that sweep up more dust as they orbit the star. Eventually, these clumps grow large enough to become planets.

A similar process should occur around supermassive black holes. These are surrounded by huge clouds of dust and gas that bear some similarities to the protoplanetary disks around young stars. As the cloud orbits the black hole, dust particles should collide and stick together forming larger clumps that eventually become blanets.

The scale of this process is vast compared to conventional planet formation. Supermassive black holes are huge, at least a hundred thousand times the mass of our Sun. But ice particles can only form where it is cool enough for volatile compounds to condense.

This turns out to be around 100 trillion kilometers from the black hole itself, in an orbit that takes about a million years to complete. Birthdays on blanets would be few and far between!

An important limitation is the relative velocity of the dust particles in the cloud. Slow moving particles can collide and stick together, but fast-moving ones would constantly break apart in high-speed collisions. Wada and co calculated that this critical velocity must be less than about 80 meters per second.

source

Black holes

A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of the region from which no escape is possible is called the event horizon. Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed. In many ways a black hole acts like an ideal black body, as it reflects no light.  

The idea of a body so massive that even light could not escape was briefly proposed by astronomical pioneer and English clergyman John Michell in a letter published in November 1784. Michell’s simplistic calculations assumed that such a body might have the same density as the Sun, and concluded that such a body would form when a star’s diameter exceeds the Sun’s by a factor of 500, and the surface escape velocity exceeds the usual speed of light.

At the center of a black hole, as described by general relativity, lies a gravitational singularity, a region where the spacetime curvature becomes infinite. For a non-rotating black hole, this region takes the shape of a single point and for a rotating black hole, it is smeared out to form a ring singularity that lies in the plane of rotation. In both cases, the singular region has zero volume. It can also be shown that the singular region contains all the mass of the black hole solution. The singular region can thus be thought of as having infinite density. 

How Do Black Holes Form?

Scientists think the smallest black holes formed when the universe began.

Stellar black holes are made when the center of a very big star falls in upon itself, or collapses. When this happens, it causes a supernova. A supernova is an exploding star that blasts part of the star into space.

Scientists think supermassive black holes were made at the same time as the galaxy they are in.

Supermassive black holes, which can have a mass equivalent to billions of suns, likely exist in the centers of most galaxies, including our own galaxy, the Milky Way. We don’t know exactly how supermassive black holes form, but it’s likely that they’re a byproduct of galaxy formation. Because of their location in the centers of galaxies, close to many tightly packed stars and gas clouds, supermassive black holes continue to grow on a steady diet of matter.

If Black Holes Are “Black,” How Do Scientists Know They Are There?

A black hole can not be seen because strong gravity pulls all of the light into the middle of the black hole. But scientists can see how the strong gravity affects the stars and gas around the black hole. 

Scientists can study stars to find out if they are flying around, or orbiting, a black hole.

When a black hole and a star are close together, high-energy light is made. This kind of light can not be seen with human eyes. Scientists use satellites and telescopes in space to see the high-energy light.

On 11 February 2016, the LIGO collaboration announced the first observation of gravitational waves; because these waves were generated from a black hole merger it was the first ever direct detection of a binary black hole merger. On 15 June 2016, a second detection of a gravitational wave event from colliding black holes was announced. 

Simulation of gravitational lensing by a black hole, which distorts the image of a galaxy in the background 

Animated simulation of gravitational lensing caused by a black hole going past a background galaxy. A secondary image of the galaxy can be seen within the black hole Einstein ring on the opposite direction of that of the galaxy. The secondary image grows (remaining within the Einstein ring) as the primary image approaches the black hole. The surface brightness of the two images remains constant, but their angular size varies, hence producing an amplification of the galaxy luminosity as seen from a distant observer. The maximum amplification occurs when the background galaxy (or in the present case a bright part of it) is exactly behind the black hole.

Could a Black Hole Destroy Earth?

Black holes do not go around in space eating stars, moons and planets. Earth will not fall into a black hole because no black hole is close enough to the solar system for Earth to do that.

Even if a black hole the same mass as the sun were to take the place of the sun, Earth still would not fall in. The black hole would have the same gravity as the sun. Earth and the other planets would orbit the black hole as they orbit the sun now.

The sun will never turn into a black hole. The sun is not a big enough star to make a black hole.

More posts about black holes

Source 1, 2 & 3

HiPOD (31 August 2018) Dunes in South Xainza Crater

   – They look so innocent… (270 km above the surface. Black and white is less than 5 km across; enhanced color is less than 1 km.)

NASA/JPL/University of Arizona

Ask Ethan: Is Spacetime Really A Fabric?

“I’d like somebody to finally acknowledge and admit that showing balls on a bed sheet doesn’t cut it as a picture of reality.”

Okay, I admit it: visualizing General Relativity as balls on a bedsheet doesn’t make a whole lot of sense. For one, if this is what gravity is supposed to be, what pulls the balls “down” onto the bedsheet? For another, if space is three dimensional, why are we talking about a 2D “fabric” of space? And for another, why do these lines curve away from the mass, rather than towards it?

It’s true: this visualization of General Relativity is highly flawed. But, believe it or not, all visualizations of General Relativity inherently have similar flaws. The reason is that space itself is not an observable thing! In Einstein’s theory, General Relativity provides the link between the matter and energy in the Universe, which determines the geometric curvature of spacetime, and how the rest of the matter and energy in the Universe moves in response to that. In this Universe, we can only measure matter and energy, not space itself. We can visualize it how we like, but all visualizations are inherently flawed.

Come get the story of how to make as much sense as possible out of the Universe we actually have.

The Planets and their respective sizes compared to our Sun.

Your Gut in Space

Finding the Right Balance for the Microbiota

Trillions of microorganisms live on and in the human body, many of them essential to its function and health. These organisms, collectively known as the microbiota, outnumber cells in the body by at least five times. 

Microorganisms in the intestinal tract, the gut microbiota, play an especially important role in human health. An investigation on the International Space Station, Rodent Research-7 (RR-7), studies how the gut microbiota changes in response to spaceflight, and how that change in turn affects the immune system, metabolic system, and circadian or daily rhythms. 

Research shows that the microbiota in the mammalian digestive tract has a major impact on an individual’s physiology and behavior. In humans, disruption of microbial communities has been linked to multiple health problems affecting intestinal, immune, mental and metabolic systems.

The investigation compares two different genetic strains of mice and two different durations of spaceflight. Twenty mice, ten of each strain, launch to the space station, and another 20 remain on the ground in identical conditions (except, of course, for the absence of gravity). Mice are a model organism that often serves as a scientific stand-in for other mammals and humans. 

Fecal material collected from the mice every two weeks will be examined for changes in the gut microbiota. Researchers plan to analyze fecal and tissue samples after 30 and 90 days of flight to compare the effects of different durations of time in space. 

With a better understanding of relationships between changes such as disruption in sleep and an imbalance of microbial populations, researchers can identify specific factors that contribute to changes in the microbiota. Further studies then can determine proactive measures and countermeasures to protect astronaut health during long-term missions. 

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Recommended Resource: The Names of God by Ken Hemphill