STARS AND GALAXIES

Prepared by:Kristine Anne P. Guindoy

IV- 6 BEED

ARTICLE

 SUPERNOVA 1987 A

The first naked – eye supernova in 383 years was discovered in the southern sky in February 1987.This steller explosion was officially named SN 1987A (SN stands for supernova and 1987 indicates that it was the first supernova observed in 1987). Naked eye super nova are rare. Only a few have been recorded in historic times. Arab observers saw one in 1006 and the Chinese recorded one in 1054 at the present location of the Crab Nebula. In addition, the astronomer Tycho Brahe observed a supernova in 1572 and Kepler saw one shortly thereafter in 1604

Prior to this event, researchers could only test their hypothesis on dim supernovae seen in distant galaxies. Thus when SN 1987A occurred, astronomers quickly focused every available telescope in the Southern Hemisphere on this spectacular event. As one astronomer remarked, “this Super nova is better studied by far than any supernova in the history”. More important this event has allowed astronomers to use observational data to test their theoretical models of stellar evolution.

Super Nova 1987A occurred about 170000 light years away in the large Magellanic Cloud, a satellite galaxy to our own Milky Way. As expected the supernova rapidly increased in brightness to a peek magnitude of 2.4, out shining all the other stars in the Large Magellanic Cloud. Also as predicted within a few weeks it began to fade. However SN 1987A did provide some surprises.

STARS

Vast number of hot, usually luminous celestial

bodies, consisting of matter and known elements and found

distributed in galaxies throughout the universe.

MEASURING DISTANCES TO

THE STARS

STELLAR PARALLAX

Extremely slight back and forth shifting in the

apparent position of a nearby star due to the

orbital motion of the Earth.

LET’S DO THIS

Close one eye and with your index finger in a

vertical position, use our eye to line up your finger

with some distant objects. Now without

moving your finger view the object with your other

eye.

PROPERTIES OF THE STARS

STELLAR BRIGHTNESS

The measure of a star’s brightness is

called it’s magnitude.

Apparent Magnitude

- A star’s brightness as it appears when viewed from earth.

Absolute Magnitude

- “true” brightness of star if it were at a standard distance of about 32.6 light years.

Name Distance Apparent Mag.

Absolute Mag.

Sun NA - 26.7 1.0

Alpha 4.27 0.0 4.4

Centauri --- --- ---

Sirius 8.70 - 1.4 1.5

Arcturus 36 - 0.1 -0.3

Betelgeuse 520 0.8 - 5.5

Deneb 1600 1.3 - 6.9

STELLAR COLOR AND

TEMPERATURE

Blue- very hot stars with surface

temp. above 30,000 K.Red- much cooler less than 3000 KYellow- temp between 5000 and 6000

K

Hertzsprung- Russell Diagram

Developed by Einar Hertzsprung and Henry Russell.

Is constructed by plotting the absolute magnitudes and temperatures of stars on a graph.

Hertzsprung- Russell Diagram

Supergiant Stars- very large stars

Giant stars- large stars

White dwarfs- very small stars

VARIaBLE STARS

Stars fluctuate in brightness. Some called pulsating variable fluctuate regularly in brightness by expanding and contracting in size.

NOVA- stars that are explosively brightens.

Interstellar Matter

New stars are born out of enormous accumulations of dust and gasses, called nebula.

This is the Helix Nebula, as imaged by the Spitzer telescope.

Two types of bright Nebulae

Emission Nebulae- derive their visible light from the fluorescence of the ultra violet light from a star in or near the nebula.

Reflection Nebulae- reflected the light nearby

stars.

STELLAR EVOLUTION

Birth Place- the birthplaces of the

stars are dark, cool, interstellar clouds which are comparatively rich in dust and gases.

Main sequence stage

From this point in the evolution of a main sequence star until its death, the internal gas pressure struggles to offset the unrelenting force of gravity.

RED GIANT STAGE

The evolution to the red giant stage results because the zone of hydrogen burning continually migrates outward, leaving behind an inert helium core.

GALAXY Is a massive, gravitationally bound

system that consists of stars and stellar remnants, an interstellar medium of gas dust, and an important but poorly understood component tentatively dubbed dark matter.

The name is from the Greek word galaxias [γαλαξίας], literally meaning "milky", a reference to the Milky Way galaxy.

 MILKY WAY GALAXY

Is a large, disk – shaped spiral galaxy about 1000,000 light years wide and about 10,000 light years thick at the center.

There are three distinct spiral arms of stars with some showing splintering.

TYPES OF GALAXIES

IRREGULAR GALAXIES- Which lack symmetry and account for only 10% of the known galaxies.

TYPES OF GALAXIES

SPIRAL GALAXIES

-Which are typically disk shaped with a somewhat greater concentrations of stars near their centers , often containing arms .

TYPES OF GALAXIES

ELLIPTICAL GALAXIES

- The most abundant type , which has an ellipsoidal shape that ranges to nearly spherical and they lack spiral arms.