black holes today

8/12/2019 Black Holes Today

1/11

Course Project | Report

Summer 09/10 Course # 140303101Astronomy & Space Sciences

InstructorDr. Humaid Majol Al-Nuaimy

StudentShatha Mohd. KarrarID # 20720984MedicineSerial # 39

University of SharjahCollege of Medicine


2/11

Introduction

How can we observe something wecant see? This is a basic questionthat rises up when studying blackholes, because according to thegeneral theory of relativity, they areregions of space of massive hugegravity from which nothing,including light, can escape. Thereason this is interesting is if these

exotic objects really do exists itgives us the opportunity to knowhow they interact with theirenvironment and helps usunderstand how they affect theformation and the evolution of thegalaxies in which they reside in.

On this paper report I cared to raise several issues concerning Black Holes, afterreading several articles, recent researches and theories. Most of these questions tilltoday riddles most of our lead astronomers and researchers, with only new answers

and theories emerging every single day. Which only just adds a new little piece of awhole uncompleted puzzle of how it all started, and from what, and where is it allgoing!

Trying to cover all the endless articles was a pure exciting challenge, because newerquestions simply never seize to end, and the theories and scientific basics theyreanswers relay on were even spectacular. Even after managing to gather all thefollowing information about black holes, some other questions still remainedunanswered, such as if black holes do evaporate, or are black holes the centralnuclei of most galaxies known, especially ours the Milky Way, and if they contributeto the formation of the galaxy it self.

But Lets not to try to jump the gun, and save these questions for later, and beginmostly with the basics to keep it simple, cause for all I can say only relying on thesebasics, we can step further from the ground to reach our unveiled answers, one dayhopefully soon!


3/11

What i s a b lack hole?

There were many popular myths concerning black holes, many of them perpetuatedby Hollywood. Movies have portrayed them as time-traveling tunnels to otherdimensions, cosmic vacuum cleaners sucking up everything in sight, and so on. Itcan be said that black holes are really just the evolutionary end point of massivestars. But somehow, this simple explanation makes them no easier to understand orless mysterious. (1)

To begin with we need to understand what a black hole really is. In many ways ablack hole is of an incredibly simple structure, in which you shall only describe 3characteristics : the mass, the spin, and the charge, but in another sense it s at thesame time a very complicated object that needs relatively complicated physics to

understand it.Black holes are the evolutionary endpoints of stars at least 10 to 15 times asmassive as the Sun. If a star that massive or larger undergoes a supernova explosion,it may leave behind a fairly massive burned out stellar remnant. With no outwardforces to oppose gravitational forces, the remnant will collapse in on itself. The stareventually collapses to the point of zero volume and infinite density, creating whatis known as a "Singularity". Around the singularity is a region where the force ofgravity is so strong that not even light can escape. Thus, no information can reach usfrom this region. It is therefore called a black hole, and its surface is called the"event horizon". (1)

Despite its invisible interior, a black hole actually can only be observed through itsinteraction with other matter. A black hole can be inferred by tracking themovement of a group of stars that orbit a region in space(especially with acompanion star).Alternatively, when gasfalls into a stellar blackhole from a companionstar, the gas spirals inward,heating to very hightemperatures and emittinglarge amounts of radiation(X-ray) that can bedetected from earth boundand Earth-orbitingtelescopes before it isswallowed completely and islost forever. (2)
http://imagine.gsfc.nasa.gov/docs/dict_jp.html#masshttp://imagine.gsfc.nasa.gov/docs/dict_qz.html#starhttp://www.cosmographica.com/gallery/portfolio2007/content/index_9.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_qz.html#starhttp://imagine.gsfc.nasa.gov/docs/dict_jp.html#mass


4/11

The Anatomy of a Black Hole

Event Horizon

All matter that comes within a certain distance of a blackhole will be trapped forever - even light, the fastestphenomenon known to exist. That distance, which can berepresented as an imaginary sphere around the black hole,is known as the event horizon. Although objects outsidethe event horizon will feel the intense gravity of the blackhole, they will be able to escape it. (6)

All matter that ventures inside the event horizon iscrushed down to a single point, at which the matter is saidto have reached infinite density. That point is known asthe singularity, which comprises the center and the very essence of the blackhole. (6)

Accretion Disk

Matter that lingers close to the black hole will spiralinward and form an accretion disk. The particles of gasand dust collide with each other as they spin around the

black hole. These collisions heat up the accretion mater,which may get so hot that it emits X-rays. (6)

Jets of Gas

Jets of hot gas are occasionally found streaming out of theregion surrounding a black hole. The gas jets flowperpendicular to the accretion disk, and they can bemillion of light years in length. This phenomenon mostlikely result from charged particles spiraling around the

intense magnetic field lines thought to rotate around ablack hole. Jets of Gas are seen around many but not allblack holes. (6)

There are other virtual concepts, boundaries and regions such as the Ergosphere and the Photon sphere that coincides with the above main structures of a blackhole.


5/11

Black holes have a broad range of masses, from the smallest (miniature) to thelargest (supermassive). Therefore there are basically three types of black holes: (6)

1) Stellar Black Holes : are such as explained above with the Companions stars.

2) Supermassive Black Holes : Fast-moving gas jets and gravitational forcesequal to millions or billions of Suns pointto the existence of huge black holes in thecenter of some galaxies. There mighteven be one in the center of our ownMilky Way galaxy. These supermassiveblack holes might be the result of thecollapse of a dense cluster of stars. (6)

3) Miniature Black Holes : Theory suggests that miniature black holes mighthave formed in the early universe. But astronomers do not have any evidenceof their existence. Miniature black holes have event horizons as small as thewidth of an atomic particle and might have been created during the Big Bang.Between 10 and 20 billion years ago, all matter and energy was compressedinto a single point. Then this

tiny point exploded (the BigBang) and expanded rapidly.Some parts might haveexpanded more rapidly thanother parts, compressing somematter and squeezing it intominiature black holes. TheseMiniature Black Holes containas much matter as Mt. Everest(a lightweight compared tonine times the mass of the

Sun!). (6)


6/11

C a n a n y o b j e c t b e c o m e a b l a c k h o l e ?

Many theories suggestedthat a black hole is a resultof an exceptionally verycompact mass, and as Prof.Andrea Ghez suggested, inorder to take a first step inunderstanding a black hole,we shall assume that it is anobjects of a mass confinedto zero volume. Thoughfortunately there is aknown virtual size thatconfines it, known as theSchwarzschild radius. At this radius, the escape speed is equal to the speed of light, andonce light passes through, it cannot escape. This Radius is of an amazing importancebecause it tells us that any given object can become a black hole! That you, yourneighborhood, your car, even your mobile device can turn in to a black hole. That isif you can simply figure out how to compress it down to the size of theSchwarzschild radius. At this point this only opens vast doors of how thegravitational force (gravity) can win over all known forces and the object wouldonly be forced to give in and collapse to an infinitely small object or Id rather say ablack hole.

This same gravitational pull makes surrounding celestial objects orbit around it.And this itself, helps us by far miles. Because once you knew how fast it orbits, youcan know the mass, and by the scale of the orbit also simply know the radius.

The Schwarzschild radius can be calculated using the equation for escape speed: (1)

vesc = (2GM/R) 1/2

For photons, or objects with no mass, we can substitute c (the speed of light) for V esc andfind the Schwarzschild radius, R, to be (1)

R = 2GM/c 2


7/11

W h a t i f t h e S u n b e c a m e a b l a c k h o l e ?

If our Sun was suddenly replaced witha black hole of the same mass, theEarth's orbit around the Sun would beunchanged. Of course the Earth'stemperature would change, and therewould be no solar wind or solarmagnetic storms affecting us. But tobe "sucked" into a black hole, one hasto cross inside the Schwarzschildradius. Now if the Sun was replacedwith a black hole that had the same

mass as the Sun, the Schwarzschildradius would be of only 3 km(compared to the Sun's radius ofnearly 700,000 km). Hence the Earthwould have to get very close to getsucked into a black hole at the centerof our Solar System. (1)

To Be More Scintefic based we canrather be assured that the Sun has nointention of doing any such thing.Only stars that weigh considerably more than the Sun end their lives as black holes. The Sunis going to stay roughly the way it is for another five billion years or so. Then it will gothrough a brief phase as a red giant star, during which time it will expand to engulf theplanets Mercury and Venus. After that, the Sun will end its life by becoming a boring whitedwarf star. (3)

But to digress. What if the Sun did become a black hole for some reason? The main effect isthat it would get very dark and very cold around here. The Earth and the other planetswould not get sucked into the black hole; they would keep on orbiting in exactly the samepaths they follow right now. Because the horizon of this black hole would be very small and

as we observed above, as long as you stay well outside the horizon & the schwarszchildradius, a black hole's gravity is no stronger than that of any other object of the same mass. (3)


8/11

" A r e b l a c k h o l e s a c t u a l l y w h i t e ? "S t e p h e n H a w k i n g ' s t h e o r y s a y s " y e s " !

Hawking has said that "black holes are not really black after all: they glow like a hotbody, and the smaller they are, the more they glow."

Stephen Hawkings great discovery was thatthe mysterious regions in space we call blackholes radiate heat through quantum effects.Hawking's famous theory says that thetemperature of a black hole varies inverselyto its mass. The mathematician Louis Craneproposed a scifi-like scenario back in 1994

that billions of years in the future, after all thestars have burned out, that small black holescould be created to generate heat andguarantee survival of the species. (4)

"Hawking famously showed that black holesradiate energy according to a thermalspectrum," said Paul Nation, an author on thepaper and a graduate student at Dartmouth."His calculations relied on assumptions about

the physics of ultra-high energies andquantum gravity. Because we can't yet takemeasurements from real black holes, we needa way to recreate this phenomenon in the labin order to study it, to validate it." (4)

The new method to create a tiny quantum sized black hole would allow researchers tobetter understand what physicist Stephen Hawking proposed more than 35 years ago: blackholes are not totally void of activity; they emit photons, which is now known as Hawkingradiation. (4)


9/11


10/11

H U B L E H U N T S D O W N B L A C K H O L E S !

Black Hole SignatureThe colorful "zigzag" is not the work of an artist.Discovered by Hubble's Space Telescope ImagingSpectrograph (STIS), these spectrographic datasuggest the existence of a supermassive blackhole. This black hole is in the center of galaxy M84.

Hubble Finds a Black HoleHubble's Wide Field and Planetary Camera

(WFPC2) can image a distant area in visible light.The telescope's Faint Object Camera (FOC) is usedto observe objects seen in ultravioletwavelengths. A composite of the core of a galaxywas produced by combining these two images.

How to Feed a Black Hole Astronomers have caught a nearby giant galaxyin the act of consuming a smaller galaxy. Thesecollisions between galaxies were common in theearly universe, when galaxies were closertogether. At the center of the giant galaxy isbelieved to be a massive black hole.Finds a BlackHole

Fireworks in Seyfert GalaxyGas blobs streaming through space at

hundreds of thousands of miles perhour can be imaged by Hubble'sSpace Telescope ImagingSpectrograph (STIS). This is thecenter of galaxy NGC4151, which isthought to house a massive blackhole.


11/11

black holes today

Documents