The Destroyer of All Matter

A black hole said to be a called a mathematical singularity, but what exactly is a singularity. The mathematics of a black hole fail to describe the shape as does the expression of 1/0. Black holes are singularities in space time. Our own milky way is said to contain a black hole in its center.

However one may ask where is the Galactic center?
The question of the finding where the galactic center is not something that is easily calculated.  However being located at the point that our solar system is, we are able to readily identify the center. Radio observations made of our galactic center reveal a highly sophisticated structure.

This image of the galactic center reveals regions of star birth never before seen.

A large number of globular clusters and gas nebulae are found at center. The above X-Ray image shows numerous stars and nebulae at the heart of our galaxy, the lighter waves on the left represent nebula's.

The above image shows a wide field view of the galactic center. Perhaps the most prominent source in this image is of Sagittarius A. Deep within Sagittarius A is the source Sagittarius A*, which astronomers have identified as being a black hole with a mass millions of times that of the Sun. Image by Dr. N.E Kassim, from data obtained by the VLAT.

The kinematics if stars within the central cluster show that the Milky Way contains a mass concentration of 4 x 10 ^ 6, this almost certainly means there is a black at the position of compact source Sagittarius A*. The acceleration of some these stars in this region have also been measured, for example one star within the region exceeded a velocity of 5000 km/s when it was closest to Sagittarius A*. Most recently in 2012 a new S-star was found with a period of only 11.5 years.

Simulation of star rotation around a black hole. The closer the star to the black hole the faster its rotation and the more space time is distorted.

 

Plot of orbits that stars orbiting Sgr* A. For some of these stars the orbit is of a high velocity while others take 10 - 14 years.

The above figure shows orbits of stars around Sagittarius A*, as determined by their proper motion and radial velocity. The black hole potential Sagittarius* A is in the center. Sagittarius A* has a proper motion of about 20km/s. You can find the full research here http://arxiv.org/pdf/0810.4674v1.pdf

A technical answer to explain a black hole would be to say, it is a solution to Einstein's theory of relativity which describes the gravitational field of mass zero.  A black hole is a compact mass that has a radius smaller than Schwarzschild radius.


The radius where the escape velocity of the black hole reaches the speed of light is called the Schwarzschild radius, named after physicist Karl Schwarzschild. The speed of light is measured to be approximately 300,000 kilometers per second.

Simulation of black hole, with gravitational lensing effect

One cannot observe the singularity at the center of a black hole. This is because when the distance of a black hole increases, the escape velocity increases, until this velocity reaches a finite speed of light and then at this point the velocity has such reached to such an extent that even light cannot escape hence making it extremely difficult to observe as no light escapes and neither does any radiation. This is one of the reasons even space telescopes cannot directly capture images of black holes, they do however find other sources of evidence that suggest and indicate the presence of black holes.

The first discussion of black holes can be traced back to famous French mathematician Pierre Simon Laplace. Fellow engineers may recall having studied Laplace Transform which is useful in analyzing electronic circuits.

Simulation of black hole creating a gravitation lensing effect, making it look as though the stars behind are bending around it.

Laplace considered that if we reduce the radius (r) of a celestial body of a mass (M), the escape velocity (Vesc) at its surface will increase. This can be written in its mathematical form below:

From this we can see that for a small radius, (Vesc) will roughly equal to the speed of light. This happens when the radius (r) decreases.

The above image shows small spiral galaxy NGC 7742. It is theorized that such type of galaxies called Seyfert type 2 are powered by a black hole in its core.

Source: Hubblesite.org

The radius of (rs) is named the Schwarzschild radius. From our above equation we can see that our radius is relatively small about 3km.

So what does this Schwarzschild equation tell us?
This equation gives us a black hole's size and the corresponding event horizon.
If we were to imagine an astronaut fall toward the event horizon, if he carried a watch it would run more and more slowly and his progress toward the event horizon would slow down as well. At the event horizon, the gravitational redshift would be so intense that the watch would stop altogether. Our astronaut would have reached the event horizon, but from our perspective he would never have made it. For the astronaut he would he would go pass the event horizon, continuously falling into the black hole for perhaps infinity. However this is our imagined scenario, because in reality the gravity at the event horizon would be so intense that our astronaut would be ripped apart atom by atom.

The above video shows very interesting simulation of a black hole with (rs) having a radius of 6.03.
At the moment it is quite difficult for us to observe the center of our galaxy but perhaps in the near future we may be able to observe this radius.

This comparison above shows four elliptical galaxies that have a massive central bulge of stars, the larger the bulge the larger the black hole. The galaxies are part of 30 galaxies searched by astronomers using NASA's Hubble Space Telescope.

The column of black-and-white pictures at left, taken by ground-based telescopes, shows the galaxies. The boxes define the central regions of stars. Close-up images of these regions, as seen by Hubble's Wide Field and Planetary Camera , are in the middle column. The column at right lists the masses of the black holes and illustrates the respective diameters of the event horizons. An event horizon defines the black hole's boundary. The event horizons cannot be seen in the Hubble images because they are about 25 million times smaller than the scale of the pictures.

Astronomers determined the mass of each black hole by measuring the motion of stars swirling around it: the closer the stars approach the black hole, the faster their velocity. The faster the stars are moving, the more massive the black hole is. This information suggests that the galaxy and the black hole grew at the same time. 

Source: Hubblesite.org

 
Black holes seem to behave like very efficient vacuum cleaners with an infinite limit. But can a black hole go away over time?

There are three stages of a black hole; stellar, primordial and super massive.

A stellar black hole is a region of space into which a star collapse's. So how does a star collapse? A start collapses once it has run out of fuel, this fuel consists of hydrogen and helium which we discussed in a previous post in Interstellar Star Formation.
It collapses to a critical size where any other type of force is overcome by a single force, gravity.

Primordial black holes are said to have been created at the time of the big bang. These mini black holes are theorized to be of the order of 1cm. In such small objects quantum theory becomes very important.  Primordial black holes could perhaps be very hot and from the outside they may actually look like a whit hole as they expel intense radiation and gamma ray bursts.

Super massive black holes are what we have been discussing earlier. These are the type that harbor in the center of galaxies. In the order of 100 million solar masses, 100 million times the size of our solar system lay at galactic nuclei.  For stellar black holes they may have a potential lifetime of 10^67 years. Most of these will have gone away by now or perhaps many lurk in far distances where there is an infancy of the universe.

Radio jets spew from Galaxy M87, on the top left we see radio emission from the elliptical galaxy. This radio source is called Virgo A. The color is in false color and highlight the intensity of the radio emission. Image courtesy of NASA, Hubble Space Telescope.

Infinitely strong gravitational forces deform and destroy matter from existence at the singularity, this is a region where physical theory breaks down. Many galaxies show an enhanced brightness in the core, along with various anomalies and high velocity of objects around it, suggest existence of a black hole. Attempts to discover black holes rely on influence of gravitational field of surrounding celestial objects. However black holes that may be easiest to discover are those within a binary system where one can easily identify its influence on its companion star.

Black hole as represented in 2014 sci-fi epic Interstellar

There are still many questions about black holes that are yet to be answered. With future development of the space telescope to succeed the Hubble Space Telescope, the James Webb Telescope is sure to uncover many more facets of the hidden secrets in universe.

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The Cosmic Microwave Background (CMB)

What is the CMB?

The radiation left from the early stages of the universe is called cosmic microwave background radiation. When the universe was at this early stage, it was soo hot that all atoms in the universe were ions. An ion is an atom that has positive and negative electrical charges. At this point in time the conditions of the universe may have been similar to that of a star; hot, dense and opaque allowing different atoms to pass through it.

Over time as the universe expanded, this gas cooled down. This ofcourse took several hundred thousand years. Radiation that was left behind from the big bang has been able to travel throughout the universe. As this early universe expanded, the radiation red-shifted to longer wavelengths and was therefore in a form to represent different temperatures. The spectrum of the CMB maintains the shape of a Blackbody spectrum. According to writer of http://hyperphysics.phy-astr.gsu.edu/hbase/mod6.html 

"Blackbody radiation refers to an object or system which absorbs all radiation incident upon it and re-radiates energy which is characteristic of this radiating system only, not dependent upon the type of radiation which is incident upon it. The radiated energy can be considered to be produced by standing wave or resonant modes of the cavity which is radiating."

The presence of CMB radiation with a Blackbody is a strong indication of the Big Bang theory. 

This above picture is a view of the sky after the foreground glow of the solar system dust has been extracted. This image is dominated by emission from interstellar dust in the Milky Way Galaxy. The two bright objects in the center of the lower right quadrant are nearby galaxies, the Large and Small Magellanic Clouds.

Source: Hubblesite.org

The COBE satellite 
The Cosmic Microwave Background Explorer was launched in 1989. Developed by NASA's Goddard Space Flight Center, its mission was to measure the infrared and microwave radiation from the early universe. COBE made some very precise measurements at different wavelengths. These measurements were from a few micrometer to 1 centimeter. 

 

The data on the graph above shows small dots, these small dots are the COBE measurement of the CMB at different frequencies. The X-Axis of the graph represents the frequency cycle per centimeter and Y-Axis represents the brightness of the frequency component. The uncertainty in each measurement is less than size of each dot. The left hand side of the curve that just begins to rise represents data points of a blackbody spectrum.  The above observation matches theoretical predictions of the Big Bang almost with perfection. So much so that there can be little doubt that one is seeing the radiation left behind from a hot, dense beginning from an earlier universe. Researches John Mather and George Smoot were awarded Nobel Prize for this work in 2006.

The above mapping shows the Northern and Southern galactic hemispheres,

Images of different regions of the hemispheres, the second image is of our galaxy. The galactic center is the middle bulged.

 

This graph displays the different magnitudes of the wavelengths from radio waves to X-rays and Gamma rays.

Image of CMB as produced by data collected byt he WMAP.

In 2001 the Wilkinson Microwave Anisotropy Probe (WMAP) made more accurate measurements of the CMB variations.  The above is much more detailed map of the structure of the universe.
In 2013, the European Space Agency (ESA) launched the Planck mission, which went one step further and obtained images in a much higher detail.

The image shows observations of the Cosmic microwave background (CMB) as observed by Planck. The image shows tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure: the stars, galaxies and nebula's that we have today.

"Most galaxies are usually in a group close by. A neighboring is never too far away. But this galaxy, known as NGC 6503, has found itself in a very lonely position, at the edge of a strange empty patch of space called the Local Void.
The Local Void is a huge stretch of space that is at least 150 million light-years across. It seems completely empty of stars or galaxies"

Source: Hubblesite.org

Star V838 Monocerotis

Source: Hubblesite.org

30 Doradus Nebula, is a giant star-forming region

Source: Hubblesite.org

 
Early scientists predicted that, the early universe must have begun as a singularity and then expanded as radiation and elementary particles. However what do we mean when we say singularity?

According to the FreeDictionary a singularity is "a hypothetical point in space-time at which matter is infinitely compressed to infinitesimal volume"
This means matter which infinitely falls toward a negative value making it smaller than any real value.

The Big Bang theory is fundamental to our understanding of the universe. So far it has resisted any efforts made by researchers to prove it false, as the CMB provides evidence of the scenario of our early universe.

The above image shows the Nucleus of Galaxy Centaurus A.

Source: Hubblesite.org
Some of the crucial discoveries made by the COBE were:

• COBE revolutionized our understanding of the early cosmological structure.
• It measured and mapped the oldest light in the universe -- the cosmic microwave background. This was similar to seeing a baby picture of the universe.
• The cmb spectrum was measured with a precision of 0.005%.
• The results confirmed the Big Bang theory of the origin of the universe.
• The very precise measurements helped eliminate a great many theories about the Big Bang.
• The mission urged scientists into a new age of precision measurements, providing ground for new research into microwave background by NASA's WMAP mission and ESA's Planck mission, that latter provided much more detailed measurements.

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Interstellar Star Formation

A star is a dense cloud of gas that produces energy in its core by fusing lighter atoms into heavier ones. This high level of energy production causes the outer layers to shine as these layers are heated to thousands of degrees Celsius. Our nearest star the Sun produces and converts around 500 million tons of hydrogen and helium every second, with only 5 million that escapes from the core and reaches us as sun light.  A few days of energy from the Sun would be enough power for all of our needs for thousands of years. Of course the challenge lies in how to preserve and manage this solar energy?

What is is the interstellar medium? The interstellar medium is the space between stars and galaxies. This matter includes a collection of gas, dust and cosmic rays. It is a region of birth for stars.

By measuring a stars color we can determine its age. Blue stars are relatively short-lived compared to the redder stars. The blue stars die off over a period of a few hundred million years, but the redder stars continue to shine for billions of years. Therefore, as a star cluster ages, its color gradually shifts from blue to red.


Source: Hubblesite.org
Perhaps one of the most iconic images by Hubble, the above image of the Eagle Nebula shows large pillars of molecular gas and dust. In this region there are many young stars, the largest pillar in the image is about 3.86243exp13 kilometers or 24 trillion miles in size.



Source: Hubblesite.org 
The above image shows area of young star formation.
These clouds are held together by self-gravity and by the intense pressure that builds up in between the clouds. This in effect causes these molecular clouds to collapse into a center, which draws gas towards inside the cloud. When the density is high enough the clouds end up fragmenting and collapsing into itself. From these clouds of dust and gas are born stars and planets.

Source: Hubblesite.org  

The above is an area in our local Large Magellanic Cloud (LMC), where there is low-mass stars with giants beside it, known as LH 95 it is about 160,000 Ly away from Earth. The image was taken by Hubble's Advanced Camera for Surveys.

From these high detail Hubble images we are looking at regions of interstellar clouds. Self-gravity is a gravitational attracting among all parts of the same object. The sum of all these forces on every other particle is exerted towards the center. This gravity can be balanced by its own structural pressure similar to how Earth is made up from rocks, or by the outward force acting on the inward force creating a balance known as hydrostatic equilibrium. If either force is unstable the star can either expand outwards on inwards into itself. However in most clouds the internal pressure pushes outward more than inward.

From the above simulation we can get an idea of where the highlighted grey blob is the Large Magellanic Cloud (LMC)  and the milky way largely visible on the right.

Source: Hubblesite.org

The densest coolest interstellar clouds are called molecular clouds because they are mainly composed of hydrogen molecules. Once these molecular clouds begin to collapse the innermost becomes a star and outer parts can become planets. The innermost part of cloud is called a protostar. The surface of a protostar is thousands of times larger then the Sun and as a result is also more luminous.




Source: Hubblesite.org

LRLL 54361 a binary protostar, it demonstrates some unknowns about star formation. The protostar emits a burst of light at intervals perhaps caused by the eccentric orbit that it may exhibit.


Source: Hubblesite.org

The above is a spectacular image of blue newly formed stars in the Small Magellanic Cloud. The Small Magellanic Cloud is in the constellation of Tucana around 200,000 Ly away. This dwarf galaxy has far less stars than compared to our own galaxy.


Even though a protostar is so bright its often the case that we cannot even see it in visible light. One of the reasons is that this light is in the infrared spectrum. Also a protostar is often buried deep within molecular clouds thus making it identifiable a difficult process. The mass of a protostar determines if it will actually become a star, as it slowly collapses, the temperature in the center rises. A newly born star continues to readjust its structure until its energy that is being radiated is the same as energy being created inside of it, this hydrostatic equilibrium is crucial.

 Simulation of Milky Way being viewed from the Small Magellanic Cloud.

Simulation of close up a globular cluster of stars, NGC 6338.

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Until next time goodbye for now.