UFO'S of UAP'S, ASTRONOMIE, RUIMTEVAART, ARCHEOLOGIE, OUDHEIDKUNDE, SF-SNUFJES EN ANDERE ESOTERISCHE WETENSCHAPPEN

What is Astrophysics? — The Hubble mosaic unveils a collection of carved knots of gas and dust in a small portion of the Monkey Head Nebula (also known as NGC 2174 and Sharpless Sh2-252). The nebula is a star-forming region that hosts dusky dust clouds silhouetted against glowing gas.
**Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)**

Astrophysics is a branch of space science that applies the laws of physics and chemistry to explain the birth, life and death of stars, planets, galaxies, nebulae and other objects in the universe. It has two sibling sciences, astronomy and cosmology, and the lines between them blur.

In the most rigid sense:

Astronomy measures positions, luminosities, motions and other characteristics
Astrophysics creates physical theories of small to medium-size structures in the universe
Cosmology does this for the largest structures, and the universe as a whole.

In practice, the three professions form a tight-knit family. Ask for the position of a nebula or what kind of light it emits, and the astronomer might answer first. Ask what the nebula is made of and how it formed and the astrophysicist will pipe up. Ask how the data fit with the formation of the universe, and the cosmologist would probably jump in. But watch out — for any of these questions, two or three may start talking at once!

Goals of astrophysics

Astrophysicists seek to understand the universe and our place in it. At NASA, the goals of astrophysics are "to discover how the universe work, explore how it began and evolved, and search for life on planets around other stars," according NASA's website.

NASA states that those goals produce three broad questions:

How does the universe work?
How did we get here?
Are we alone?

It began with Newton

While astronomy is one of the oldest sciences, theoretical astrophysics began with Isaac Newton. Prior to Newton, astronomers described the motions of heavenly bodies using complex mathematical models without a physical basis. Newton showed that a single theory simultaneously explains the orbits of moons and planets in space and the trajectory of a cannonball on Earth. This added to the body of evidence for the (then) startling conclusion that the heavens and Earth are subject to the same physical laws. [Related: How Isaac Newton Changed the World]

Perhaps what most completely separated Newton’s model from previous ones is that it is predictive as well as descriptive. Based on aberrations in the Newtonian orbit of Uranus, astronomers predicted the position of a new planet, which was then observed and named Neptune. Being predictive as well as descriptive is the sign of a mature science, and astrophysics is in this category.

Milestones in astrophysics

Because the only way we interact with distant objects is by observing the radiation they emit, much of astrophysics has to do with deducing theories that explain the mechanisms that produce this radiation, and provide ideas for how to extract the most information from it. The first ideas about the nature of stars emerged in the mid-19th century from the blossoming science of spectral analysis, which means observing the specific frequencies of light that particular substances absorb and emit when heated. Spectral analysis remains essential to the triumvirate of space sciences, both guiding and testing new theories.

Early spectroscopy provided the first evidence that stars contain substances also present on Earth. Spectroscopy revealed that some nebulae are purely gaseous, while some contain stars. This later helped cement the idea that some nebulae were not nebulae at all — they were other galaxies!

In the early 1920s, Cecilia Payne discovered, using spectroscopy, that stars are predominantly hydrogen (at least until their old age). The spectra of stars also allowed astrophysicists to determine the speed at which they move toward or away from Earth. Just like the sound a vehicle emits is different moving toward us or away from us, because of the Doppler shift, the spectra of stars will change in the same way. In the 1930s, by combining the Doppler shift and Einstein’s theory of general relativity, Edwin Hubble provided solid evidence that the universe is expanding. This is also predicted by Einstein’s theory, and together form the basis of the Big Bang Theory.

Also in the mid-19th century, the physicists Lord Kelvin (William Thomson) and Gustav Von Helmholtz speculated that gravitational collapse could power the sun, but eventually realized that energy produced this way would only last 100,000 years. Fifty years later, Einstein’s famous E=mc² equation gave astrophysicists the first clue to what the true source of energy might be (although it turns out that gravitational collapse does play an important role). As nuclear physics, quantum mechanics and particle physics grew in the first half of the 20th century, it became possible to formulate theories for how nuclear fusion could power stars. These theories describe how stars form, live and die, and successfully explain the observed distribution of types of stars, their spectra, luminosities, ages, and other features.

Astrophysics is the physics of stars and other distant bodies in the universe, but it also hits close to home. According to the Big Bang Theory, the first stars were almost entirely hydrogen. The nuclear fusion process that energizes them smashes together hydrogen atoms to form the heavier element helium. In 1957, the husband-and-wife astronomer team of Geoffrey and Margaret Burbidge, along with physicists William Alfred Fowler and Fred Hoyle, showed how, as stars age, they produce heavier and heavier elements, which they pass on to later generations of stars in ever-greater quantities. It is only in the final stages of the lives of more recent stars that the elements making up the Earth, such as iron (32.1 percent), oxygen (30.1 percent), silicon (15.1 percent), are produced. Another of these elements is carbon, which together with oxygen, make up the bulk of the mass of all living things including us. Thus, astrophysics tells us that, while we are not all stars, we are all stardust.

Ariel Balter has a Ph.D. in physics. He teaches and writes about science.

Further reading

A History of Astrophysics

The Glassmaker Who Sparked Astrophysics

IN BRIEF

A new paper asserts that a physical body might be able to pass through a wormhole in spite of the extreme tidal forces that are at play.

A physical object, such as a person or a spacecraft, could theoretically make it through a wormhole in the centre of a black hole, and maybe even access another universe on the other side, physicists have suggested.

In what looks like the logical extension of the plot of Interstellar – where astronauts try to hunt down another universe after the catastrophic effects of climate change destroy Earth – physicists have modelled what would happen to a chair, a scientist, and a spacecraft, if each one ended up inside the spherical wormhole of a black hole.

“What we did was to reconsider a fundamental question on the relation between the gravity and the underlying structure of space-time,” said one of the team, Diego Rubiera-Garcia from the University of Lisbon in Portugal.

“In practical terms, we dropped one assumption that holds in general relativity, but there is noa priori reason for it to hold in extensions of this theory.”

So let’s take a step back first, and go through some of the basics. According to Einstein’s theory of general relativity, at the centre of a black hole lies a singularity – the point at which the forces of gravity are at their most intense, and time and space effectively end.

Watch: What are Wormholes?

If an object approaches the event horizon, it would be crushed in one direction, and stretched in another, thanks to the extreme tidal forces of gravity at play inside a black hole. If the object stays intact long enough to make it to the centre of a black hole, it will be infinitely long and thin: basically, it’s been spaghettified beyond recognition.

Physicists have been playing around with the assumption of a singularity in the centre of a black hole for years, because until we can actually prove it exists, there could be any number of possibilities that still work – in theory.

Earlier this year, physicists from the University of Cambridge in the UK argued that there’s no reason why a singularity necessarily has to be on the inside of a black hole. They suggest that in a universe with five or more dimensions – which isn’t out of the question for us – a ‘naked’ singularly could exist, which is not bound by an event horizon.

Of course, this would mean big, huge things for our current understanding of how the laws of physics govern our Universe, because it basically needs Einstein’s theory of general relativity to be wrong.

“If naked singularities exist, general relativity breaks down,” said one of the team, Saran Tunyasuvunakool, back in January. “And if general relativity breaks down, it would throw everything upside down, because it would no longer have any predictive power – it could no longer be considered as a standalone theory to explain the Universe.”

If you feel you are in a black hole, don’t give up. There’s a way out.

Einstein being wrong isn’t out of the question, either. Stephen Hawking has been battling for decades with the way general relativity appears to clash with quantum mechanics in black holes – a problem known as the information paradox.

So assuming that the stipulations of general relativity aren’t set in stone, the new study from Rubiera-Garcia’s team argue that if you remove singularity from a black hole, what you get in the centre instead is a finite-sized wormhole.

Then, they figured out what could happen if various objects – a chair, a scientist, and a spacecraft – made it beyond the event horizon and into the wormhole. These objects are referred to as ‘observers’.

They modelled these observers as an aggregation of points connected by physical or chemical interactions that hold everything together as the object travels along a geodesic line. A geodesic line is simply the path in spacetime that a free-falling object follows.

“Each particle of the observer follows a geodesic line determined by the gravitational field,”says Rubiera-Garcia. “Each geodesic feels a slightly different gravitational force, but the interactions among the constituents of the body could nonetheless sustain the body.”

Publishing in the journal Classical and Quantum Gravity, the researchers demonstrate this by showing how the time spent by a light ray in a round trip between two parts of the body is always finite.

This means that finite forces, no matter how strong, could compensate for the impact of the gravitational field near and inside the wormhole on a physical body travelling through it.

“Thus, different parts of the body will still establish physical or chemical interactions and, consequently, cause and effect still apply all the way across the throat of the wormhole,” they explain.

So while the theory of general relativity predicts that an object approaching a black hole will be crushed along one direction and stretched along another infinitely, if we assume that the centre of a black hole is a wormhole with a finite radius, the object can only be crushed just as much as the size of the wormhole.

This means according to Rubiera-Garcia’s hypothesis, an object could survive a journey through a wormhole and make it out the other side – and potentially to another universe – technically intact, but it would be crushed to the size of the finite wormhole. At least it’s not completely destroyed, right?

“For a theoretical physicist, the suffering of observers is admissible (one might even consider it part of an experimentalist’s job) but their total destruction is not,” Rubiera-Garcia and his team quip in an opinion piece.

Until we figure out how to actually see a black hole, all of this is going to remain well and truly in the realm of pure hypotheticals. But we’re beginning to see how black holes might not be the horrible, existence-obliterating death traps we thought they were.

As Hawking said at a conference back in August 2015 about his solution to the information paradox: “The message of this lecture is that black holes ain’t as black as they are painted. They are not the eternal prisons they were once thought. … If you feel you are in a black hole, don’t give up. There’s a way out.”