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PRESENTATION ON “QUASARS”

PREPARED BY : SANCHITA CHETRI

CLASS : MSC 4^TH SEMESTER

ROLL NO : 21UMPY18

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WHAT IS QUASARS?

QUASARS MEANS QUASI-STELLAR RADIO SOURCES. IT IS THE MOST LUMINOUS POWERFUL AND ENERGETIC OBJECT SEEN IN THE UNIVERSE.
IT IS A ENERGY IN THE FORM OF ELECTROMAGNETIC RADIATION BEING RELEASED FROM THE COLLISION OF MATTER(PARTICLES, GASES,STARS) ORBITING SUPERMASSIVE BLACK HOLES NEAR THE EVENT HORIZON
THE BRIGHTEST QUASAR KNOWN IS CALLED 3C 273 AND IS IN THE CONSTELLATION VIRGO.

HISTORY OF OBSERVATIONS�

AROUND 1930’s , KARL JANSKY DISCOVERED STATIC INTERFERENCE ON THE TRANSATLANTIC LINES COMING FROM THE MILKY WAY.
IN 1950’s, THESE LUMINOUS OBJECTS WERE DISCOVERED BY THE EARLY RADIO SURVEYS OF THE SKY.
MARTEEN DISCOVERED THE PATTERN OF THE EMISSION LINES IN THE BRIGHTEST QUASAR COMING FROM THE HYDROGEN ATOMS.

HOW ARE QUASARS FORMED?

BEFORE GOING TO FORMATION OF QUASARS, WE NEED TO KNOW “WHAT IS BLACK HOLE?”
BLACK HOLE IS A PLACE IN SPACE WHERE GRAVITY PULLS SO MUCH THAT EVEN LIGHT CAN NOT GET OUT. IT DOESN’T EMIT ANY LIGHT, BUT ASTRONOMERS DETECT THE LIGHT USING THEIR QUASARS AND GRAVITATIONAL FIELD.
IT IS A POINT WHERE ALL THE MASS AND ENERGY COLLAPSED UNDER ITS OWN WEIGHT DUE TO GREATER GRAVITATIONAL FORCE.
THE STARS AT THEIR TIME OF DEATH WENT TO FORM BLACK HOLES, GIVING RISE TO SUPER MASSIVE BLACK HOLES.
THE BLACKHOLES THEN INHALED MORE MATTER AND THIS THEN BECAME THE SIZE WE SEE TODAY i.e. THE QUASARS

OPTICAL PROPERTIES

QUASARS SHOW STRONG UV EMISSION UNLIKE THE NORMAL STARS BECAUSE NORMAL STARS ON THE ABSORPTION OF BALMER LINES NEAR 3700, DONOT SHOW UV EXCESS LIKE THE QUASARS.
THE COLOUR-COLOUR DIAGRAM OF QSO’s IS SHOWN IN THE FIG.
THE MAIN SEQUENCE STARS YIELD A CURVE SHOWS THE

BLACKBODY LINE AE. THE QUASARS ARE PLACED ON THE

EITHER SIDES OF BLACKBODY LINE, BUT ALL THE QUASARS

ARE PLACED ABOVE THE MAIN SEQUENCE CURVE.

THE REDSHIFT OF QUASARS

REDSHIFTS IS THE DISPLACEMENT OF THE SPECTRUM OF AN ASTRONOMICAL OBJECT TOWARD LONGER(RED) WAVELENGTH.
ONE OF THE BEST CRITERIA FOR THE IDENTIFICATION OF QUASARS IS THE DETECTION OF LARGE REDSHIFTS Z, EXHIBITED IN THEIR OPTICAL SPECTRA.
Their redshifts are measured from the strong spectral lines that dominate their visible and ultraviolet spectra. All observed quasar spectra have redshifts between 0.056 and 7.54.
THE REDSHIFT CAN ALSO BE DEDUCED FROM EINSTEIN’S THEORY OF GENERAL RELATIVITY. IN THIS CASE, THE REDSHIFT OF AN OBJECT WHOSE MASS IS M AND RADIUS R IS GIVEN BY:
Z = GM/Rc²

Where g is the gravitational constant and c is the velocity of light.

Z = 1.47 * 10⁵ M/RM_O

ACCORDING TO FEW ASTRONOMERS , THE LARGE REDSHIFTS OBSERVED IN THE SPECTRA OF QUASARS ARE DUE TO THE EXPANSION OF THE UNIVERSE.
THE LUMINOSITY IS DEPENDED UPON THE DISTANCES OF THE QUASARS. i.e. IF ASSUMED COSMOLOGICAL, THE OBJECTS MUST BE VERY LUMINOUS.
THEY ARE EVEN VISIBLE AT GREAT DISTANCES BECAUSE THEY EMIT ENOUGH AMOUNTS OF ENERGY AND ARE CERTAINLY NOT STARS.

ACTIVE GALACTIC NUCLEI

A QUASAR IS AN ACTIVE GALACTIC NULCEUS (AGN) THAT IS BRIGHT WAY ABOVE THE AVERAGE.
QUASARS ARE 100,000 TIMES BRIGHTER THAN THE MILKY WAY GALAXY.
AT THE CENTER OF A GALAXY, WE CAN USUALLY FIND A SUPERMASSIVE BALCK HOLE. THIS IS CALLED A GALACTIC NUCLEUS. WHEN THIS NUCLEUS PULLS A LOT OF DUST,GAS, AND OTHER MATERIALS, THE FORCES EXERTED CREATE SO MUCH FRICTION A HUGE AMOUNT OF LIGHT IS EMITTED ALL ACROSS THE EM SPECTRUM. THIS IS CALLED AN AGN

PROPERTIES

THE QUASAR’S LUMINOSITY IS ABOUT 4 TRILLION (4*10¹²) TIMES THAT OF OUR SUN, OR ABOUT 100 TIMES THAT OF THE TOTAL LIGHT OF GIANT GALAXIES LIKE OUR MILKY WAY.
THE HUGE LUMINOSITY OF QUASARS RESULTS FROM THE ACCRETION DISK OF CENTRAL MASSIVE BLACK HOLES
QUASARS SHOW THE LOCATIONS WHERE MASSIVE BLACK HOLES ARE GROWING RAPIDLY.
LUMINOSITIES VARIES WITH TIME.
IT GETS ENERGY WHEN MATTER FALLS INTO A MASSIVE BLACK HOLES