Category: astrophysics

AR9077: Solar Magnetic Arcade On July 14…

AR9077: Solar Magnetic Arcade

On July 14th, solar active region 9077 (AR9077) produced a massive flare. The event also blasted an enormous cloud of energetic charged particles toward planet Earth, triggering magnetic storms and dramatic auroral displays. This striking close-up of AR9077 was made by the orbiting TRACE satellite shortly after the flare erupted. It shows million degree hot solar plasma cooling down while suspended in an arcade of magnetic loops. 

Credit: TRACE, Stanford-Lockheed ISR, NASA

What is a protostar?The formation of stars beg…

What is a protostar?

The formation of stars begins with the collapse and fragmentation of molecular clouds into very dense clumps.  These clumps initially contain ~0.01 solar masses of material, but increase in mass as surrounding material is accumulated through accretion.  The temperature of the material also increases while the area
over which it is spread decreases as gravitational contraction
continues, forming a more stellar-like object in the process.  During
this time, and up until hydrogen burning begins and it joins the main sequence, the object is known as a protostar.

This stage of stellar evolution may last for between 100,000 and 10 million years depending on the size of the star being formed. If the final result is a protostar with more than 0.08 solar
masses, it will go on to begin hydrogen burning and will join the main
sequence as a normal star.  For protostars with masses less than this,
temperatures are not sufficient for hydrogen burning to begin and they
become brown dwarf stars.

Protostars are enshrouded in gas and dust and are not detectable at visible wavelengths.  To study this very early stage of stellar evolution, astronomers must use infrared or microwave wavelengths.

Protostars are also known as Young Stellar Objects (YSOs).

Solar Prominence A prominence is a large,…

Solar Prominence

A prominence is a large, bright, gaseous feature extending outward from the Sun’s surface, often in a loop shape. Prominences are anchored to the Sun’s surface in the photosphere, and extend outwards into the Sun’s corona. While the corona consists of extremely hot ionized gases, known as plasma, which do not emit much visible light, prominences contain much cooler plasma, similar in composition to that of the chromosphere. The prominence plasma is typically a hundred times more luminous and denser than the coronal plasma. (source

animation:

Chuck Manges

What are nebulas?. And why nebulas are big as …

What are nebulas?. And why nebulas are big as galaxies.

Basically, a nebula a huge cloud of gas and dust. Some nebulae are the rest of the death of a giant star, like a supernova. Other nebulae are where new stars are forming. (more)

The nebulae are divided into some types:

  • Emission Nebulae
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Emission nebulae are gas clouds with high temperature. The atoms in the cloud are energized by ultraviolet light from a nearby star and emit radiation when they decay to lower energy states. Emission nebulae are usually red, because of hydrogen, the most common gas in the Universe and commonly emitting red light.

  • Reflection nebulae
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Reflection nebulae are dust clouds that simply reflect the light of a star or nearby stars. Reflection nebulae are usually blue because the blue light is spread more easily. Emission and reflection nebulae are usually seen together and are sometimes called diffuse nebulae.

  • Dark nebulae
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There are also dark nebulae, they are clouds of gas and dust that almost completely prevent the light from passing through them, are identified by the contrast with the sky around them, which is always more starry or bright. They may be associated with star formation regions.

  • Planetary nebulae
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Planetary nebulae were named after William Herschel because when they first appeared to the telescope, they resembled a planet, later it was discovered that they were caused by ejected material from a central star. This material is illuminated by the central star and shines, and an emission spectrum can be observed. The central star usually ends up as a white dwarf.

  • Remnant of supernova
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Remnant of supernova is a gas envelope, composed of the remains of a star that was destroyed by a violent explosion, supernova, marking the death of this.

Theoretically, what would happen if two black …

Theoretically, what would happen if two black holes were next to each other or crossing paths?

Theoretically the collision of black holes gives rise to gravitational waves, and is one of the most extreme events of the universe.

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The result of the collision of two black holes results in a single black hole and its mass is somewhat smaller than the sum of the masses of both, the rest is released in the form of energy ie gravitational waves.

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Por exemplo: two black holes — of 36 and 29 solar masses — merging into a single 62 solar mass one. Those missing three solar masses? They were converted into pure energy: gravitational waves rippling through the fabric of space.

The diffuse heliospheric current extends to th…

The diffuse heliospheric current extends to the outer regions of the Solar System, and results from the influence of the Sun’s rotating magnetic field on the plasma in the interplanetary medium. source.

I was wondering if you could go in depth, at l…

I was wondering if you could go in depth, at least to a degree about how incredibly dense objects have strong enough gravity to distort light. To me that's one of the wildest concepts I can imagine, not that I expect you to be all knowing but maybe you've got a good article or something? I don't recall if you've ever made posts about the theory of relativity. Sorry for the long ask!

Well, I know only the basics, things I study in my free time, however, I can try to explain. The distortion of space-time is described by Einstein’s Theory of General Reality. The more massive an object, the more its curvature will be in the space-time fabric.

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This distortion in light is known as a gravitational lensing. The gravitational lensing is formed due to a space-time distortion caused by the presence of a large mass body between a distant light source and an observer.

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These distortions are widely observed through globular clusters.

Since the amount of lensing depends on the total mass of the cluster, gravitational lensing can be used to ‘weigh’ clusters. This has considerably improved our understanding of the distribution of the ‘hidden’ dark matter in galaxy clusters and hence in the Universe as a whole. The effect of gravitational lensing also allowed a first step towards revealing the mystery of the dark energy.

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As gravitational lenses function as magnification glasses it is possible to use them to study distant galaxies from the early Universe, which otherwise would be impossible to see.

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Gravitational lensing happens on all scales – the gravitational field of galaxies and clusters of galaxies can lens light, but so can smaller objects such as stars and planets. Even the mass of our own bodies will lens light passing near us a tiny bit, although the effect is too small to ever measure.

What would cause two stars to collide? What do…

What would cause two stars to collide? What does it take for a whole planet (as massive as Jupiter) to change trajectory?

The main mechanism that would make two stars collide is gravity. This depends on several factors, some stars may wander through space and end up being attracted by the gravitational field of another star, from there, one star begins to orbit the other. 

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But the most common are collisions in clusters of stars, because in a star cluster the stars are very close together, especially in globular clusters. 

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Collisions of young stars may also occur, as most of the stars are born close to each other in clusters. Many stars are binary, formed together, but in some cases before they evolve they may end up colliding.

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In the universe both collisions of active stars can occur, as can collisions of white dwarfs, neutron stars and black holes.

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The orbits of the planets are determined by the gravitational pull of the Sun, so it would need some very extreme force to cause the orbit of a planet to change its trajectory, perhaps if some planet or star enters our solar system, or when the Sun goes through changes and become a white dwarf in about 5 billion years.

Milky Way’s Biggest Globular Cluster Unlikel…

Milky Way’s Biggest Globular Cluster Unlikely to Host Habitable Exoplanets

Close encounters between stars in Omega Centauri, the only star cluster visible to the naked eye, leave little room for habitable planets, according to new research.

In the hunt for habitable exoplanets, Omega Centauri, the largest globular cluster in the Milky Way, seemed like a good place to look. Comprising an estimated 10 million stars, the cluster is nearly 16,000 light years from Earth, making it visible to the naked eye and a relatively close target for observations by the Hubble Space Telescope.

Starting with a rainbow-colored assortment of 470,000 stars in Omega Centauri’s core, the researchers homed in on 350,000 stars whose color—a gauge of their temperature and age—means they could potentially harbor life-bearing planets.

For each star, they then calculated the habitable zone—the orbital region around each star in which a rocky planet could have liquid water, which is a key ingredient for life as we know it. Since most of the stars in Omega Centauri’s core are red dwarfs, their habitable zones are much closer than the one surrounding our own larger sun.

“The core of Omega Centauri could potentially be populated with a plethora of compact planetary systems that harbor habitable-zone planets close to a host star,” Kane said. “An example of such a system is TRAPPIST-1, a miniature version of our own solar system that is 40 light years away and is currently viewed as one of the most promising places to look for alien life.”

Ultimately, though, the cozy nature of stars in Omega Centauri forced the researchers to conclude that such planetary systems, however compact, cannot exist in the cluster’s core. While our own sun is a comfortable 4.22 light years from its nearest neighbor, the average distance between stars in Omega Centauri’s core is 0.16 light years, meaning they would encounter neighboring stars about once every 1 million years.

“The rate at which stars gravitationally interact with each other would be too high to harbor stable habitable planets,” Deveny said. “Looking at clusters with similar or higher encounter rates to Omega Centauri’s could lead to the same conclusion. So, studying globular clusters with lower encounter rates might lead to a higher probability of finding stable habitable planets.” source

Relativistic Jets Super-massive black hol…

Relativistic Jets

Super-massive black holes in the centers of some active galaxies create powerful jets of radiation and particles travelling close to the speed of light. Attracted by strong gravity, matter  falls towards the central black hole as it feeds on the surrounding gas and dust. But instead of falling into the black hole, a small fraction of particles get accelerated to speed almost as great as the speed of light and spewn out in two narrow beams along the axis of rotation of the black hole. These jets are believed to be the sources of the fastest-travelling particles in the Universe – cosmic rays.

In some cases these jets can reach outside of the galaxy itself, ending in giant radio lobes far from the active galaxy center. Observed with radio telescopes these galaxies can have a variety of shapes, mostly resembling dumbbells. We call these objects either radio galaxies or quasars, depending on how bright they are and how fast they consume the surrounding matter. As these monster black holes grow to become a billion times more massive than our Sun, their jets eventually get strong enough to blow gas out of the galaxy and shut off the formation of new stars! 

A small fraction of active galaxies with jets are oriented so that their jet is pointed straight at Earth. In those cases we observe radiation across the electromagnetic spectrum enhanced by the enormous speed of the jet and call such sources blazars. By combining NuSTAR X-ray observations with observations in the radio, visible light and extremely energetic gamma-rays, we are learning about the physics of how powerful jets are formed and sustained. One of the remaining mysteries is how do jets create radiation of such extraordinary broad spectrum up to very high energies.

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