New apps available on Universe.

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Alez
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#1 New apps available on Universe.

Post by Alez »

BHspin V2

As you might have noticed we added a new application recently. It is devoted to investigate the spin evolution of black holes.

When a black hole accretes matter, at the same time it accretes the angular momentum, which results in faster spinning. In this model we examine the influence of this process. What makes it particularly interesting is the fact the the LIGO observatory of gravitational waves started to operate recently. Therefore, in the near future, our theoretical predictions will be checked against observation.

Wojciech Gładysz, who cooperates with us in this project prepared a longer description of this problem which I posted in the Science section. I invite you to take a look.
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Alez
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#2 Re: New apps available on Universe.

Post by Alez »

Written by Wojciech Gładysz

There are many words one could use to describe a black hole: strange, bizzare or out of this world. These are all valid terms, but they are not
very specific. You cannot objectively measure the strangeness of a black hole, so scientists had to come up with a different idea for escribing
those esoteric objects.

Black holes, as we now know, can be fully described by three numbers: their mass, their spin and their electric charge. Astrophysical black holes (the ones we are dealing with in our research) are believed to have almost no electric charge, so our description simplifies. We are generally very happy when something gets simpler, but the original difficulty of the problem greatly reduces the excitement.

Let's say we want to know the mass and the spin of a given black hole. First, we need to find it! It emits no light and almost no radiation
(except for the Hawking one that we do not know how to measure), so it does not make our job easy. The only possible way of finding one, in the vastness of space, is by looking at its gravitational interactions with "visible" objects (such as the stars). Therefore, interacting binary
systems are the best cosmic laboratories available for the study of black holes.

The mass part of a black hole is pretty simple - we can calculate it once we know the mass of its companion star and the parameters of the binary system they form (e.g. the separation of the objects). What about its spin? And, what is more important, what is this spin you've been reading about? Spin is nothing more than a fancy name for angular momentum. Our planet rotates and thus have certain angular momentum - undisturbed, it will continue keeping the same angular momentum forever. This is because in our Universe angular momentum is conserved! If you'd like to change the rotational motion of the Earth, you'd have to act on it by an external torque (an asteroid maybe?). The spin of a black hole is therefore a measure of how fast this black hole rotates.

There are at least three observational methods which allow you to estimate the spin. None of them is perfect and the underlying physical principles are greatly simplified. Therefore, the obtained spin values are very uncertain. That is why we want to examine how our astrophysical evolutionary models fit into that picture. I used the word "models" on purpose - there is a bunch of them. When a star interacts with a black hole, it can transfer its mass and make the black hole heavier. This flowing mass carries momentum and may increase the spin of the black hole. But the question is - what fraction of this flowing mass is transferred to the black hole? 100% or maybe 50%? And what was the initial spin of a black hole when it first formed? How the spin evolution would be affected by changing its initial value from 0 to 0.5 on a 0-1 scale? The initial spin value is still an open question in astrophysics. If we found a binary system in which a black hole would be fed solely by stellar wind coming from its companion and would be highly spinning, this would mean that the spin comes from earlier evolutionary stages and is inborn rather than acquired by mass accretion (which in the case of stellar-wind-fed systems is negligible).

Black holes in interacting binaries may be fed by stellar winds coming from their companions and by more direct mass transfers (the so-called Roche Lobe overflows). We have models ready to examine the influence of these two physical phenomena on the spin evolution. This is what we want to examine with your help!
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#3 Re: New apps available on Universe.

Post by Alez »

Universe QuarkStar

We have just started the tests of a new application. The main goal is to analyse the possibility of observational detection of quark stars. These objects are composed of quarks, i.e. particles smaller than neutron or proton. Quark stars are nearly similar to neutron stars, but we may observe their impact on stellar populations.

Quark Stars have been proposed to explain observations of very massive neutron stars, but these objects are hardly distinguishable from each other. The population studies are necessary, which will be probably available soon with Square Kilometre Array (SKA). However, a lot of theoretical study have to be done before any information may be dug out from observations. This is the goal of Quark Star application. Nevertheless, we are pioneers in such studies so a lot of tests is yet in front of us, before a large scale computation could be started.
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#4 Re: New apps available on Universe.

Post by Alez »

The reionisation project

The results of the Universe@Home project will be used by the University of Cambridge! The cooperation will concern the reionisation of the Universe throughout the cosmic time. This process has a huge impact on the evolution of stars and galaxies.
Although University of Cambridge has a vast computational power, the number of project run on their computers and other problems made Universe@Home a promising alternative.
We will let you know about the details of the project as soon as we obtain the first results.

The early universe is thought to have been a dynamic place, and about 13 billion years ago, it underwent a so-called age of re-ionization. During this period, the universe's fog of hydrogen gas was clearing and becoming translucent to ultraviolet light for the first time.
What have driven the age of re-ionization is indeed a well-known problem, which is still unresolved. We hope that Universe@Home will help to shed some light on it!

Scientists have long been puzzled over what caused this re-ionization to occur space.com
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