21) Message boards : News : Recognition for gravitational waves discovery (Message 1180)
Posted 17 May 2016 by Grzegorz Wiktorowicz
Post:
I have a pleasure to inform you, unless you already know, that prof. Krzysztof Belczyński,
the PI of Universe@Home project, in recognition for his involvement in discovery of gravitational
waves, was awarded recently with the Medal of Nicolas Copernicus and the Breakthrough Prize.

The former is the most prestigious prize awarded by the Polish Academy of Sciences. The latter is an
international award bestowed for remarkable scientific outcome. It was awarded for the whole group,
which took part in the research.

The results from the Universe@Home project are still used to increase our understanding of
gravitational waves and their role in the Universe.

-------------------

Mam przyjemność poinformować Was, choć możliwe, że już wiecie, że prof. Krzysztof Belczyński,
kierownik projektu Universe@Home, w uznaniu swoich zasług w odkryciu fal grawitacyjnych, został
nagrodzony Medalem im. Mikołaja Kopernika i Breakthrough Prize.

Pierwsza nagroda jest najbardziej prestiżą przyznawaną przez Polską Akademię Nauk. Druga
natomiast to międzynarodowa nagroda przyznawana za znaczące odkrycia naukowe. Została ona
przyznana całej grupie biorącej udział w badaniach.

Wyniki otrzymywane w ramach projektu Universe@Home są ciągle używane do poszerzania naszej
wiedzy na temat fal grawitacyjnych i ich roli we Wszechświecie.
22) Message boards : News : Black hole merger (PL: Koalescencja czarnych dziur) (Message 1148)
Posted 20 Apr 2016 by Grzegorz Wiktorowicz
Post:
Wersja polskojęzyczna poniżej

You have already heard about the discovery of gravitational waves from a merger
of double black hole. In our project, specifically in the BHspin application, we
were also working on the evolution of such systems. If you are interested in the
way how they form and evolve, we prepared for you the description of the evolution of
a typical system, which results in the emission of gravitational waves like these
from the recent observations. You may found the text, together with a nice plot,
in the forum's science section. Please enjoy!


Prawdopodobnie wiecie już o odkryciu fal grawitacyjnych z koalescencji czarnych
dziur. W naszym projekcie, a konkretnie za pośrednictwem aplikacji BHspin,
analizowaliśmy ewolucję takich systemów. Jeżeli jesteście zainteresowani tym jak
podwójne czarne dziury się tworzą, to przygotowaliśmy dla was opis
popularnonaukowy jednego z typowych systemów. Jego ewolucja prowadzi do emisji
fali grawitacyjnej jak ta z niedawnych obserwacji. Tekst razem z poglądowym
rysunkiem można znaleźć na forum w dziale Science. Zapraszamy!
23) Message boards : Science : Black hole merger - evolution (EN+PL) (Message 1147)
Posted 20 Apr 2016 by Grzegorz Wiktorowicz
Post:

Powyższy rysunek (wykonany przez Wojciecha Gładysza) przedstawia ewolucję
typowego systemu, który emituje silne promieniowanie grawitacyjne w ciągu
swojego życia. Lewa kolumna podaje wiek systemu. W centrum znajduje
się uproszczony rysunek fazy ewolucyjnej ze stanem ewolucyjnym gwiazd i ich
masami (Po lewo dla pierwszej (głównej) gwiazdy, a po prawo dla towarzysza).
Prawa kolumna przedstawia odległość między gwiazdami w jednostkach promienia
Słońca i ekscentryczność, która opisuje eliptyczność orbity (0.00 oznacza orbitę
kołową). Poniżej znajdziecie krótki opis ewolucji przedstawionej na tym rysunku.


Opis ewolucji układu podwójnego prowadzący do koalescencji dwóch czarnych dziur
w ciągu wieku Wszechświata

Ciąg główny wieku zerowego (początek ciągu głównego; ZAMS) może być postrzegany jako
moment narodzin układu podwójnego. Wtedy gwiazdy zaczynają syntezę helu w swoich
jądrach, a to oznacza początek najdłuższej fazy ewolucyjnej w ich życiu,
tak zwanego ciągu głównego (MS). Gwiazda na ciągu głównych świeci niemal
jednostajnie.

Sytuacja zmienia się jednak drastycznie gdy w jądrze zaczyna brakować paliwa
wodorowego. Im cięższa jest gwiazda tym ten moment nadchodzi szybciej. Dla
masywnej pierwszej gwiazdy ciąg główny kończy się po paru milionach lat.
Następnie jądro gwiazdy się kurczy i jednocześnie rozgrzewa. Natomiast wodorowa
otoczka się nadyma i staje się nawet 100 razy większa niż na ciągu głównym! Ta
krótka lecz bardzo dynamiczna faza ewolucji jest nazywana przerwą
Hertzsprunga
(HG).

W tak olbrzymiej gwieździe jej najbardziej zewnętrzne warstwy przestają
być związane grawitacyjnie z jądrem. Taka materia może zostać przechwycona przez
pole grawitacyjne drugiej gwiazdy i opaść na nią zwiększając jej masę. Taki
przepływ masy jest znany jako wypełnienie powierzchni Roche'a (RLOF). Trwa on zaledwie
kilkaset lat ale jest dość silny by odwrócić stosunek mas, tj. gwiazda główna,
która była prawie dwukrotnie cięższa na początku ciągu głównego, teraz jest
blisko dwa razy lżejsza.

W wyniku przepływu materii gwiazda główna zostaje całkowicie pozbawiona wodorowej
otoczki i staje się gwiazdą helową o masie około 25 razy cięższej od Słońca.
Taka gwiazda, po krótkiej ale drastycznej utracie masy w wietrze gwiazdowym,
tworzy czarną dziurę w wyniku bezpośredniego kolapsu. "Bezpośredni" oznacza to,
że nie ma wybuchu supernowej, gdyż pole grawitacyjne tworzącego się obiektu jest
zbyt duże by pozwolić jakiejś materii ulecieć w przestrzeń.

Towarzysz, który był lżejszy na początku ciągu głównego, ewoluuje wolniej.
Jednak, po około 6 milionach lat, ta gwiazda również kończy fazę spalania wodoru
(ciąg główny) i rozpoczyna ekspansję. W przeciwieństwie do opisanego powyżej
transferu materii, w tym wypadku stabilny przepływ masy nie jest możliwy. Czarna
dziura nie jest w stanie pochłonąć całej dopływającej do niej masy traconej
przez towarzysza i obie gwiazdy zostają otoczone przez wspólną otoczkę (CE). Pomimo
tego, że ta faza jest niesamowicie krótka (trwa mniej niż 1000 lat), to znacząco
zmienia ona postać systemu. Po pierwsze, towarzysz traci swoją wodorową otoczkę
i staje się gwiazdą helową o masie większej niż 20 mas Słońca. Tak samo jak w
przypadku pierwszej gwiazdy tak i w przypadku drugiej zachodzi bezpośredni jej
kolaps do czarnej dziury. Drugim rezultatem wspólnej otoczki jest olbrzymia
utrata momentu pędu i związane z tym zacieśnianie się systemu. Odległość między
gwiazdami spada z 2000 promieni słońca do zaledwie 25! Na koniec cała wspólna
otoczka zostaje odrzucona z systemu.

Otrzymaliśmy w ten sposób układ dwóch czarnych dziur na względnie bliskiej
orbicie (10% odległości z Ziemi do Słońca!). Taka konfiguracja pozwoli na dalsze
zacieśnianie orbity na skutek emisji fal grawitacyjnych, które unoszą moment
pędu i energię orbitalną). Po 5.4 miliardach lat (prawie połowa wieku
Wszechświata), nastąpi koalescencja, której będzie towarzyszyła krótka ale
wybuchowa emisja fal grawitacyjnych, podobna do tej która została niedawno
zaobserwowana.
24) Message boards : Science : Black hole merger - evolution (EN+PL) (Message 1146)
Posted 20 Apr 2016 by Grzegorz Wiktorowicz
Post:

The plot above (credits to Wojciech Gładysz) presents the evolution of a
particular system which emits strong gravitational on the way. The leftmost
column provides the system age. In the centre we have the simplified plots of
the binary with evolutionary phase and mass (in solar units) of the primary (on
the left) and the secondary (on the right). The rightmost column presents the
separation (distance between the stars) in the solar radius units and the
eccentricity, which describes how elliptic is the orbit (0.00 means a circular
orbit). Below you can find the short description of the system's evolution.


The description of a binary evolution leading to the merger of two black holes
within the age of the Universe

The Zero Age Main Sequence (ZAMS) may be perceived as a birth time of a binary.
At this moment the stars start the helium synthesis inside their cores. This
marks also the beginning of the longest phase in their lifespan, the so-called
Main Sequence (MS). The star on the main sequence shines nearly invariably.

The situation changes abruptly when the hydrogen fuel becomes depleted in the
core. The heavier the star the earlier it occurs. For a massive primary the main
sequence ends after a few million years. Afterwards, the core starts to collapse
and heats considerably, whereas the star's envelope swells and becomes even 100
times larger! These very short but extremely dynamic phase is called the
Hertzsprung Gap (HG).

In such a large star it is easy for the outermost layers to become unbound with
the core. Then, the free-floating matter may be caught by the gravitational
field of the secondary and fall on it enlarging its weight. This mass transfer
is known as a Roche lobe overflow (RLOF). Lasting only a few hundred years, it
is strong enough to reverse the mass ratio, i.e., the primary, which was nearly
two times heavier on ZAMS, now is nearly two times lighter.

As the outcome of the RLOF the primary is totally stripped of its outer hydrogen
envelope and becomes a bare helium star of a mass of about 25 solar masses. Such
a star, after a brief episode of strong mass loss due to stellar wind, forms a
black hole (BH) through a direct collapse. 'direct' here means that no
supernova explosion is observed as the gravitational field of the new-formed
object is to large to allow any matter to be ejected from the system.

The secondary, which was lighter on ZAMS, evolves less rapidly. However, after
about 6 million years of evolution, it also ends the hydrogen burning phase (the
main sequence) and commences the expansion. But, in contrast to the RLOF phase
explained above, currently no stable mass transfer is possible. The primary is
unable to accrete all the mass, which is lost by the secondary and the two stars
become engulfed by this matter. We obtain the phase known as the Common Envelope
(CE). Although being extremely short (less than 1000 years), the phase alters
the system significantly. Firstly, the secondary loses the hydrogen envelope and
becomes a helium star more than 20 times heavier than the Sun. As it occurred to
the primary, such a star cannot live long and soon collapses to form a black
hole. Secondly, the common envelope takes away a lot of angular momentum from
the binary, which results in a large orbit shrinkage (from ~2000 solar radii to
~25 solar radii). Finally, all the common envelope matter becomes repelled from
the system.

We reached the double black hole system on a relatively close orbit (~10% of the
distance between the Earth and the Sun!). Such a configuration will allow for
the further tightening of the orbit due to gravitational waves emission (they
take away angular momentum and orbital energy). In the end, after 5.4 billion
years (nearly half the age of the Universe) the merger will occur accompanied
with a strong burst of gravitational emission, which may be observable on the
Earth.
25) Message boards : News : Gravitational waves vs. StarTrack code (Message 1074)
Posted 19 Feb 2016 by Grzegorz Wiktorowicz
Post:
You have probably heard about the outstanding discovery of gravitational waves announced a week ago (e.g., http://www.nature.com/news/einstein-s-gravitational-waves-found-at-last-1.19361). It is a milestone in our understanding of the Nature. Universe@Home was not involved directly in the detection, but it is relevant to highlight, that already in year 2010, prof. Belczyński predicted, that the first gravitational waves observation will involve a double black hole merger, whereas most of the scientists claimed that it will concern a merger of neutron stars. The original paper can be found here: http://adsabs.harvard.edu/abs/2010ApJ...715L.138B.

Please observe that prof. Belczyński used then the same StarTrack code that we are using in the Universe@Home project! Of course, now we have a bit updated version. Therefore, the recent discovery proved the reliability of our methods!

If you like to learn more about gravitational waves, I recommend a thorough but comprehensible introduction by the discoverers http://www.ligo.org/science.php.
26) Message boards : News : New models and television program about U@H (in polish) (Message 1032)
Posted 21 Jan 2016 by Grzegorz Wiktorowicz
Post:
We have finished a bunch of models, which will be published shortly. However, still a lot more are waiting for investigation. In the case of ULXs we are working on the influence of more primordial matter composition on formation of these mysterious objects. The BHSPIN application concentrate on black holes spin (i.e., rotation), which influences the mass accretion processes (necessary for the detection of this latent objects), and emission of gravitational waves (a.k.a. propagation of space-time wrinkles). The last process is recently raises a unprecedented interest due to the rumours of its first observations. Predicted 100 years (precisely) gravitational waves have not been detected yet. Our results may play a significant role in understanding the observational results.

In polish public television appeared in the end of previous year a program about scientific computing considering also our project. Unfortunately it is available only in polish. You may found it here https://www.youtube.com/watch?v=iZIkjBXrcMM
27) Message boards : News : New ULX application (Message 801)
Posted 24 Nov 2015 by Grzegorz Wiktorowicz
Post:
Last week we prepared the ULX application which is closely related to the previous (now obsolete) X-ray application. It is investigating the possibility of connecting the Ultraluminous X-ray sources (ULX) with X-ray binaries (XRB). We want to make a comprehensive study far wider than the one from the test project which was published in September.

ULXs are one of the greatest conundrums currently investigated in astronomy and every month new observations are coming up. Our code is the best to deal with the problem of their nature from the theoretical side. ULXs are very rare systems. In our simulations only 1 XRB per 100 have a very short phase of such a high emission and only in some particular models.

If you have any questions of comments concerning this application, please put them in this thread.
28) Message boards : News : New BHspin application (Message 799)
Posted 24 Nov 2015 by Grzegorz Wiktorowicz
Post:
Sorry to all for this problem and thanks for notifying us! We were trying to find out where the problem lies but up to now we don't know. On our test computers we didn't encounter such problems. Probably some systems in a very uncommon case go into endless loop. In the future version of the code, which should be prepared in a few/several weeks, we will add additional output to investigate this problem.

Currently the data from this BHspin application is strongly needed by ongoing project connected with the observations of gravitational waves. As you may know the LIGO observatory have just started to operate after significant upgrades and a lot of people are looking forward to first results.

If you keep obtaining this error with BHspin app, please switch to ULX. We hope that this problem will be solved soon.
29) Message boards : Science : Black hole spins (Message 738)
Posted 12 Nov 2015 by Grzegorz Wiktorowicz
Post:
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 describing
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!
30) Message boards : News : New BHspin application (Message 737)
Posted 12 Nov 2015 by Grzegorz Wiktorowicz
Post:
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.

I hope that you will become interested in this research!
31) Message boards : News : New code (Message 624)
Posted 20 Oct 2015 by Grzegorz Wiktorowicz
Post:
We have made significant upgrades to the code, removed a few bugs, and incorporated new additional physics to widen our field of research.

Due to this fact we delete the remaining work units. These which are currently processed by users will stay unharmed and the points will be added as before. Tomorrow we will compile the new code and prepare new workunits.

If you find any problems with the new code, please let us know.
32) Message boards : Science : Universe X-ray sources (Message 583)
Posted 5 Oct 2015 by Grzegorz Wiktorowicz
Post:
Hello!

Currently we are not planning that. However, the algorithm is perfect for GPU-computing and in the future we will for sure consider such an improvement.
33) Message boards : News : New code (Message 543)
Posted 17 Sep 2015 by Grzegorz Wiktorowicz
Post:
We have just finished the primary tests of the new version of the code. This gave us a green light to start the computation of a grid of models. We want especially to test the brand new approach to the mass transfer between stars in binary systems and the physics of accretion onto compact objects (i.e., neutron stars and black holes). These processes have a fundamental role during the evolution of binaries. Moreover, they also influence the evolution of whole galaxies and even the Universe itself.

As soon as partial results will be obtained and analysed, we will provide you with more details and news.

Thanks for you help!
34) Message boards : Science : Universe X-ray sources (Message 542)
Posted 16 Sep 2015 by Grzegorz Wiktorowicz
Post:
Sorry for this silence on the forum. We are working on the introduction of the new code for the simulations. It will, hopefully, allow for long, uninterrupted calculations of several different models and investigation of a bunch of astrophysical problems. I will write a news today about that.

Concerning this a bit farcical file names, they were introduced just for easier recognition. This particular one is the model in which we investigate the influence of a different initial distribution of eccentricities for low-mass stars. It was proposed and developed by a person whose name is Paulina. We cooperate with her but she is not a member of the team (yet).

Don't hesitate to ask if you have further questions.
35) Message boards : Science : Typical evolutionary routes of EULXs (Message 433)
Posted 23 Jul 2015 by Grzegorz Wiktorowicz
Post:

Above you may find the schematic evolution of a binary system leading to the
formation of Extreme Ultraluminous X-ray sources (EULX) with neutron star (NS)
accretors. I assume that you have read the post about BH EULX. A lot of
definitions and processes are similar, so I tried to avoid the repetitions
except if they are practical.

We start with far lighter stars than in the case of BH EULX. The primary on
ZAMS is 10 times larger than the Sun whereas the secondary is 5.6 times
larger. The semi-major axis is also smaller in this case. The only similarity
is the significant eccentricity of the orbit.

Lighter stars evolve slower. The primary runs out of hydrogen in the core
after about 24 million years. It expands and the matter from its outer layers
becomes unbound and falls on the secondary. We acquire the mass transfer. Due
to the tidal interactions the orbit becomes circular (e=0) and therefore
smaller, but the loss of mass leads to orbit expansion. Parallelly, masses of
the stars change strongly.

The primary, which is now only 2 times the mass of the Sun, becomes the
subject of a very specific type of supernova explosion, the so called
Electron-Capture Supernova (ECS). The outcome is the NS with a mass of 1.26
solar masses (very typical mass for NS).

Neutron stars, in contrast to BH, born with a significant natal kick. This
means that they obtain additional velocity due to the asymmetry of the SN
explosion. This results in a slight distortion of the orbit.

Just like in the case of BH, in absence of a companion, a neutron star will
not change. However, evolving companion starts to expand (due to the lack of
thermonuclear fuel), enters the Giant Branch phase (more long lasting and
stable phase than HG which it proceeds) and engulf the NS with its envelope.
We acquire the Common Envelope (CE) phase which strongly shortens the
separation between stars and lowers the mass of the secondary.

Afterwards we are left with an unaffected NS and a companion which is
consisted of helium and heavier elements. The secondary commences the helium
burning in its core in thermonuclear reactions producing carbon. However,
after a few million years, the star runs out of this fuel also and, just like
in the case of hydrogen, starts to expand. The phase is known as Helium
Hertzsprung Gap (HeHG).

In the end, the mass transfer starts due to the strong gravitational field of
NS which strips the outer layers from the secondary star. Just like in the
case of the BH, NS is very small, whereas the infalling gas possesses a lot of
angular momentum. Therefore, the accretion disk (AD) forms, which is the
source of X-ray radiation. Such a stellar configuration provides an extremely
large mass transfer rate, but on a very short timescale (~100 years). Such a
situation may occur in a large number of systems, thus we are able to observe
them.
36) Message boards : Science : Typical evolutionary routes of EULXs (Message 431)
Posted 21 Jul 2015 by Grzegorz Wiktorowicz
Post:
You are right Sebastian. We showed that regular compact objects are adequate to obtain EULXs and we do not need to introduce IMBH, which are still hypothetical objects.

The times on this chart are the time since ZAMS or the age of the system, which we defined to be the same. The ZAMS is the moment when the object starts to fulfil the definition of the star, so it is a best place to be marked as zero age.

As far as this difference in maximum luminosity is concerned, there appeared a small confusion. These are only typical(!) routes and it is not obvious if the inferred characteristics apply to the whole population of objects. For example BH accretors acquire higher luminosities in spite of the fact that comparing typical systems we may come up with different conclusion. On the other hand, you are right that BHs have lower mass-to-energy conversion efficiency due to the lack of solid surface.
37) Message boards : Science : Universe X-ray sources (Message 427)
Posted 18 Jul 2015 by Grzegorz Wiktorowicz
Post:
Einstain@home is a totally different project. Firstly, they concentrate on the search for gravitational waves. Secondly, they process observations.

Nevertheless, we can cooperate. For example, we can predict what they should obtain. Some predictions for the gravitational radiation have been made with StarTrack code already (e.g., Figure 13 of http://arxiv.org/pdf/1110.1726v1).
38) Message boards : News : Poster (Message 426)
Posted 18 Jul 2015 by Grzegorz Wiktorowicz
Post:
In the Science thread I posted the description of the typical evolutionary route leading to the formation of EULX system. I invite you to take a look.
39) Message boards : News : Poster (Message 425)
Posted 18 Jul 2015 by Grzegorz Wiktorowicz
Post:
Yes, you are right. BOINC is very interesting on its own and, as I have written, people during the conference were very interested about it. I just doubt if they will be eager to buy the poster about our results. It is not a custom to buy, or even take, posters presenting work of someone else.

Concerning the screensaver, of course we intend to include it into this project and we have some interesting ideas. For example, the screensaver can present the evolution of interesting systems that are being currently computed. I think that it may be interesting. However, due to other more important work the screensaver has been postponed.
40) Message boards : Science : Typical evolutionary routes of EULXs (Message 424)
Posted 18 Jul 2015 by Grzegorz Wiktorowicz
Post:

Above you see a graphic which presents the main phases of the typical
evolution of a binary systems which leads to the formation of Extreme
Ultraluminous X-ray Source.

We start on ZAMS. These acronym stands for Zero Age Main Sequence. Speaking
shortly, this means the beginning of the thermonuclear reactions in the
stellar core. The ZAMS is the time in which the star produces its first light.
The mass and matter composition on ZAMS, in absence of interactions with other
objects, totally determines the further evolution of the star.

In our case on ZAMS we have two massive stars. One is 33 times heavier than
Sun and the second "just" 11 times. 'a' stands for semi-major axis (i.e., mean
distance between stars), which is quite moderate: 5500 solar radii (nearly the
distance from Sun to Neptune). 'e', on the other hand, is the eccentricity,
which describes how strongly the orbit is ellipsoidal (e=0 is equivalent to
circular orbit). Value e=0.56 means that the orbit is highly ellipsoidal and
the stars during one orbital period approach and move away from one another
significantly changing the separation.

The heavier star in a binary is usually called the 'primary'. The heavier the
star, the faster it evolves. Primary quickly burns out all the Hydrogen (the
thermonuclear fuel), in its core, and starts to expand. Meanwhile its core
shrinks and worms up. At some point the temperature becomes high enough to
start the synthesis of helium. The phase is called Core Helium Burning (CHeB).
The continuous expansion leads to the situation in which the envelope of the
primary starts to engulf the secondary. We reach the Common Envelope (CE)
phase after 5.5 million years of evolution.

Common envelope is a highly important phase in the evolution of binaries,
because it is responsible for shrinking of the orbit, which allows for
interaction between stars. In our case it decreases the semi-major axis 100
times. After CE the primary is just the naked core composed mainly by elements
heavier then hydrogen, because its envelope was repelled from the system.
Afterwards, it quickly evolves to supernova explosion (SN).

Supernova (pl. supernovae) is second most important step on our way. The
massive evolved star ejects its outer layers in a very energetic way. The
release of energy is comparable with the luminosity of the whole galaxy. It
lefts the compact remnant (a neutron star (NS) or a black hole (BH)) or
possibly can destroy the star completely. In our case the BH is formed. The
orbit is slightly altered due to explosion but the companion is nearly
unaffected.

If not the secondary, the BH will be the final step in the life of primary.
However, it is not in our case. The second star evolves slower and comes on
the stage several million years after the primary's SN. It runs out of
hydrogen and starts to expand. This phases is called Hertzsprung Gap (HG). It
is very short and is characterised by a very dynamic expansion of outer
layers, which become only slightly bound with the central parts of the star.

At some point the gravitation of the BH will overcome the gravitation of the
HG star and the matter will start to fall on the compact star. We will obtain
the mass transfer between the stars. Due to the fact that the black hole is a
very small object (about several kilometres in diameter) and the infalling
matter possesses a significant amount of angular momentum, an accretion disk
(AD) forms around the BH.

In the AD happens the most important phenomena for our case. Due to the
viscosity of matter, the kinetic energy is transformed to thermal energy. Gas
warms up and approaches the BH. Near the centre of the disk the temperature
reaches millions of Kelvins and is therefore a source of X-ray radiation. We
obtain the X-ray Binary.

In EULXs the mass transfer rate is so strong that the amount of X-ray
radiation exceeds predictions of all hitherto used model. Nevertheless, the
phase is very short (10,000 yr) in the comparison with the stellar evolution
scales. However, our results showed, that the models are not in contradiction
with observations and we are able to explain what we see.


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