Twinkle, twinkle, little starTwinkle, twinkle, little star, How I wonder what you are. Up above the world so high, Like a diamond in the sky. Twinkle, twinkle, little star, How I wonder what you are! (Jane Taylor wrote the lyrics in 1806)http://kids.niehs.nih.gov/games/songs/childrens/twinklemid.htm

BINTANG Sebiji bola gas yang panas dan bercahaya di angkasa lepas membebaskan haba dan cahayanya sendiri. Tenaga dihasilkan melalui tindak balas nuklear.

Terdiri daripada terutamanya hidrogen dan helium. Stars produce energy by nuclear fusion of hydrogen into helium.

Matahari ialah bintang yang paling dekat dgn. Bumi. Bintang-bintang lain terletak sangat jauh dari Bumi, oleh itu kelihatan sebagai titik-titik cahaya sahaja.

Pada waktu malam yang tidak berawan, cuma dengan mata kasar kita dapat melihat sebanyak 3000 bintang di langit. Dengan menggunakan teleskop lebih daripada sejuta bintang dapat dilihat. Contoh: Bintang dedua (binary stars) iaitu dua bintang yang berputar mengelilingi satu sama lain, bintang kerdil putih, bintang neutron,

Properties of StarsBinary stars and stellar mass Binary stars Two stars orbiting one another Stars are held together by mutual gravitationBoth orbit around a common center of mass

Properties of StarsBinary stars and stellar mass Binary stars Visual binaries are resolved telescopicallyMore than 50% of the stars in the universe are binary starsUsed to determine stellar massStellar massDetermined using binary starsThe center of mass is closest to the most massive star

Binary Stars Orbit Each Other Around Their Common Center of Mass

Properties of StarsStellar mass Mass of most stars is between one-tenth and fifty times the mass of the Sun The more massive a star is, the brighter it is

L ~ M3.5

How Far Away Are Stars?The distance to a star is measured inlight-years. A light-year is the distance that light travels in one year. About 5.8 trillion miles (9.5 trillion kilometers).

The nearest star (besides our sun) is 4.24 light-years from earth.This means that light emitted for this star takes 4.24 years to reach earth.

Some stars are over millions of light-years away. The closest star is the Sun. (150 juta km)Beyond that is Proxima Centauri, at 4.24 light-years away. (40 trillion km)Alpha Centauri is at 4.37 light-years, and beyond that is Barnard's star at 5.97 light-years away.

Properties of Stars Parallax Astronomers often used parallax to measure distances to nearby stars.The nearest stars have the largest parallax angles, while those of distant stars are too small to measure.

Parallax cannot be used to measure distances any greater than 1000 light years using existing technology.Too small to measure accurately.

ParallaxParallax is the slight shifting of the apparent position of a star due to the orbital motion of Earth. (viewed from two different positions. (The less the star appears to move, the farther away it is.)

Distances to StarsTrigonometric Parallax:Star appears slightly shifted from different positions of the Earth on its orbitThe farther away the star is (larger d), the smaller the parallax angle p.d = __ p 1 d in parsec (pc) p in arc seconds1 pc = 3.26 LY0

The Trigonometric ParallaxExample:Nearest star, a Centauri, has a parallax of p = 0.76 arc secondsd = 1/p = 1.3 pc =1.3 x 3.26 = 4.3 LYWith ground-based telescopes, we can measure parallaxes p 0.02 arc sec=> d 50 pcThis method does not work for stars farther away than 50 pc.0

Properties of Stars Light-Year A light-year is the distance light travels in a year, about 9.5 trillion kilometers in one year. (Light travels at 300,000 km/s)Jarak bintang dari Bumi diukur dalam unit tahun cahayaSatu tahun cahaya ialah jarak yang dilalui oleh cahaya dalam masa satu tahun.

Proxima Centauri is 4.3 light years away (40 trillion km) Nearest star to Earth other than the Sun (150 juta km)

Properties of Stars Matahari berada 150 juta km dari Bumi. Jika cahaya bergerak dengan kelajuan 300,000,000 ms-1 (300,000 km/s)Berapa lamakah masa yang diambil untuk cahaya Matahari sampai ke Bumi?

Masa = jarak = 150, 000, 000 km kelajuan 300, 000 kms1

= 500 s = 8.33 minit

Properties of Stars Star Color and Temperature Color is a clue to a stars temperature.Hot stars are blue-white colourCool star looks orange or redStars that have same temperature as the Sun have a yellow colour

Properties of Stars Color and temperature Hot star Temperature above 30,000 K (>25,000C)Emits short-wavelength lightAppears blue-white eg. RigelCool star Temperature less than 3000 K (< 3500 C)Emits longer-wavelength lightAppears red/orange eg. BetelgeuseBetween 5000 and 6000 K (same temperature as the Sun)Stars appear yellow

Lifetimes of StarsHow long a star lives depends on how much mass it has. Stars age at different rates. Massive stars use fuel faster and exist for only a few million years (shorter lifetime). Small stars use fuel slowly and exist for perhaps hundreds of billions of years. Medium-mass stars like the sun live for about 10 billions years. Astronomers think the sun is about 4.6 billion years old, so it is almost halfway through its lifetime.

Masses of Stars in the H-R DiagramHigh-mass stars have much shorter lives than low-mass stars:Sun: ~ 10 billion yr.10 Msun: ~ 30 million yr.0.1 Msun: ~ 3 trillion yr.Low massesHigh massesMasstlife ~ M-2.50

25.1 Properties of Stars Apparent Magnitude (Magnitud ketara) Apparent magnitude is the brightness of a star when viewed from Earth. Three factors control the apparent brightness of a star as seen from Earth: how big it is, how hot it is, and how far away it is. Absolute Magnitude (Magnitud mutlak) Absolute magnitude is the apparent brightness of a star if it were viewed from a distance of 32.6 light-years. Is a measure of the amount of light it gives off.

Properties of Stars Stellar brightness Apparent magnitude (mV) Brightness when a star is viewed from EarthDecreases with distanceNumbers are used to designate magnitudesDim stars have large numbers and negative numbers are also used

Properties of Stars Stellar brightness Absolute magnitude (MV ) "True" or intrinsic brightness of a starIs a measure of the amount of light it gives off.Brightness at a standard distance of 32.6 light-yearsMost stars' absolute magnitudes are between 5 and +15

Distance, Apparent Magnitude, and Absolute Magnitude of Some StarsRigel -distance from Earth = 900 light years app mag (mV) =0.14, abs mag (MV) = - 6.8

Distance and Intrinsic/Absolute BrightnessBetelgeuseRigelExample:App. Magn. mV = 0.41Recall that:App. Magn. mV = 0.14For a magnitude difference of 0.41 0.14 = 0.27, we find an intensity ratio of (2.512)0.27 = 1.280

Magn. Diff.Intensity Ratio12.51222.512*2.512 = (2.512)2 = 6.315(2.512)5 = 100

Distance and Intrinsic Brightness (2)BetelgeuseRigelRigel is appears 1.28 times brighter than Betelgeuse,Thus, Rigel is actually (intrinsically) 1.28*(1.6)2 = 3.3 times brighter than Betelgeuse.but Rigel is 1.6 times further away than Betelgeuse.0

Absolute Magnitude (2)BetelgeuseRigelBack to our example of Betelgeuse and Rigel:Difference in absolute magnitudes: 6.8 5.5 = 1.3 => Luminosity ratio= (2.512)1.3 = 3.30mV = apparent magnitude MV = absolute magnitude

BetelgeuseRigelmV0.410.14MV-5.5-6.8d152 pc244 pc520 LY900 LY

Hertzsprung-Russell Diagram A HertzsprungRussell diagram shows the relationship between the absolute magnitude (luminosity) and temperature of stars (spectral class). A main-sequence star is a star that falls into the main sequence category on the HR diagram. This category contains the majority of stars and runs diagonally from the upper left to the lower right on the HR diagram.

Idealized Hertzsprung-Russell Diagram About 100 years ago, Ejnar Hertzsprung in Denmark and Henry Norris Russell in USA made graphs to find out if temperature and brightness is related. The graph is still used by astronomers and is called H-R diagram.

Hertzsprung-Russell Diagram Shows the relation between stellar Luminosity (brightness) and absolute magnitude)Temperature and spectral class

Diagram is made by plotting (graphing) each star's Luminosity (brightness) andTemperature

Hertzsprung-Russell Diagram Parts of an H-R diagram Main-sequence stars (bintang jujukan utama)90% of all starsBand through the center of the H-R diagramSun is in the main-sequence

Giants (or red giants) A red giant is a large, Very luminousCool LargeUpper-right on the H-R diagram

Hertzsprung-Russell Diagram Very large giants are called supergiantsA supergiant is a very large, very bright red giant star.Only a few percent of all starsWhite dwarfsFainter than main-sequence starsSmall (approximately the size of Earth)Lower-central area on the H-R diagramNot all are white in colorPerhaps 10% of all starsSusunan bintang menurut saiz Bintang neutron

Organizing the Family of Stars: The Hertzsprung-Russell DiagramWe know: Stars have different temperatures, different luminosities, and different sizes. To bring some order into that zoo of different types of stars: organize them in a diagram of LuminosityversusTemperature (or spectral type)LuminosityTemperatureSpectral type: O B A F G K MHertzsprung-Russell DiagramorAbsolute mag.0

Komposisi kimia yang membina sebuah bintang berbeza mengikut kelasnya. Rujuk Jadual Spectral type: O B A F G K MKomposisi ini ditentukan dgn mengkaji spektrum cahaya bintang tersebut

KELASKOMPOSISI KIMIAO (biru)Helium terion, atom helium, sedikit hidrogenB (biru-putih)Atom helium , hidrogenA (putih)Hidrogen, Kalsium terionF (kuning)Kalsium terion, hidrogen

G Jingga)Kalsium terion, hidrogen, logam terutamanya ferumK (Jingga-merah)Logam, kumpulan CH dan CNM (merah)Titanium oksida

HertzsprungRussell DiagramIn general, stars with higher temperature also have brighter absolute magnitudesMain sequence band(jujukan utama) contains hot, blue, bright stars in the upper left and cool, red, dim stars in the lower right while the yellow star, sun fall in between.

Hertzsprung-Russell Diagram To which group do most stars belong? a. supergiants b. giants c. main sequence d. white dwarfsWhich star is hotter than the Sun? a. Betelgeuse b. Aldebaran c. Alpha Centauri B d. Sirius BWhich star is most likely to be red? a. Rigel b. Sirius A c. Sirius B d. BetelgeuseCompared to Rigel, Alpha Centauri B is a. cooler and brighter b. cooler and dimmer c. hotter and brighter d. hotter and dimmer5. Which star has a greater absolute magnitude? a. Rigel b. Aldebaran c. Sirius B d. Betelgeuse

Properties of Stars Interstellar MatterA nebula is a cloud of gas and/or dust in space. There are two major types of nebulae:1. Bright nebula Such as Orion Nebula and Eagle Nebula contain hot glowing gases that are forming into stars. 2. Dark nebulaContain cool gases - Emission nebula - Reflection nebula

Interstellar Matter

The Orion Nebula Is a Well-Known Emission Nebula

Nebula, Birthplace of StarsGlobules = sites where stars are being born right now!Trifid Nebula

Stellar Evolution Stars exist because of gravityTwo opposing forces in a star are GravityContractsThermal nuclear energyExpandsStagesBirthIn dark, cool, interstellar cloudsGravity contracts the cloudTemperature risesBecomes a protostar

Stellar Evolution StagesProtostar Gravitational contraction of gaseous cloud continuesCore reaches 10 million KHydrogen nuclei fuseBecome helium nucleiProcess is called hydrogen burning Energy is releasedOutward pressure balanced by gravity pulling inStar becomes a stable main-sequence star90% of a star's life is in the main-sequence

Formation of a StarInterstellar Cloud (cloud of gas and/or dust)

Collapsing cloud fragment

Fragmentation ceases A protostar (developing star not yet hot enough to engage in nuclear fusion)

Protostellar evolution (Temp.10 million K, pressure within is so great that nuclear fusion of hydrogen begins)

A Newborn star

Star died

Stellar Evolution Protostar Stage A protostar is a collapsing cloud of gas and dust destined to become a stara developing star not yet hot enough to engage in nuclear fusion. When the core of a protostar has reached about 10 million K, pressure within is so great that nuclear fusion of hydrogen begins, and a star is born.

Kelahiran BintangBintang dipercayai berasal daripada Nebula (kepulan awan besar yang terdiri daripada gas hidrogen dan debu)Gas hidrogen dan debu itu terkumpul akibat daya tarikan graviti antara gas dan debu. Semakin banyak gas dan debu terkumpul, semakin kuat tarikan graviti yang terhasil. Nebula mengecut secara berterusan dan termampat menjadi protostar.Daya tarikan graviti yang semakin bertambah menyebabkan suhu dan tekanan pada teras semakin meningkat.Apabila suhu dan tekanan dalam teras cukup tinggi, pelakuran nuklear gas hidrogen berlaku dan menghasilkan helium dan banyak haba dan cahaya. Bola gas itu mula bersinar dan sebuah bintang dilahirkanProses kelahiran ini mengambil masa berjuta-juta tahun lamanya.

Kelahiran Bintang

Kelahiran BintangNebula

Daya graviti

Penyejatan

Pengecutan

Jasad bintang

ProtostarsProtostars = pre-birth state of stars:Hydrogen to Helium fusion not yet ignitedStill enshrouded in opaque cocoons of dust => barely visible in the optical, but bright in the infrared.

Heating By ContractionAs a protostar contracts, it heats up:Free-fall contraction Heating0 K = -273 CX - A young protostar begins as an invisible concentration of gas deep inside a cloudY- A contracting protostar grows hotter but is hidden inside its dusty cocoon and is detectable only in infraredZ - A newborn star becomes visible as it blows its dust cocoon away.XYZ

Protostellar DisksConservation of angular momentum leads to the formation of protostellar disks birth place of planets and moons

From Protostars to StarsIgnition of H He fusion processesStar emerges from the enshrouding dust cocoonMo solar massThe most massive stars contract to the main sequence over 1000 times faster than the lowest mass stars .

Death of the Star (The End of a Stars Life)When all the nuclear fuel in a star is used up, gravity will win over pressure and the star will die.High-mass stars will die first, in a gigantic explosion, called a supernova.Less massive stars will die in a less dramatic event, called a nova

Stellar Evolution (Death of the Star)

Stellar Evolution All stars, regardless of their size, eventually run out of fuel and collapse due to gravity. Stars less than one-half the mass of the sun never evolve to the red giant stage but remain in the stable main-sequence stage until they consume all their hydrogen fuel and collapse into a white dwarf. White dwarf cools to become black dwarf. Death of Low-Mass Stars

Stellar Evolution Stars with masses similar to the sun evolve in essentially the same way as low-mass stars. During their collapse from red giants to white dwarfs, medium-mass stars are thought to cast off their bloated outer layer, creating an expanding round cloud of gas called planetary nebula.Medium-mass star Between 0.5 and 3 solar massesRed giant collapsesPlanetary nebula forms Becomes a white dwarf

Life Cycle of a Sunlike Star

The Fate of Our Sun and the End of EarthSun will expand to a Red giant in ~ 5 billion yearsExpands to ~ Earths radiusEarth will then be incinerated!Sun may form a planetary nebula (but uncertain)Suns C,O core will become a white dwarf

Planetary Nebula

25.2 Stellar Evolution In contrast to sun-like stars, stars that are over three times the suns mass have relatively short life spans, which end in a supernova event. Death of Massive StarsA supernova is an exploding massive star that increases in brightness many thousands of times. The massive stars interior condenses and may produce a hot, dense object that is either a neutron star or a black hole.

Crab Nebula in the Constellation TaurusSupernova of 1054.

Stellar Remnants White Dwarfs A white dwarf is a star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size, believed to be near its final stage of evolution. The sun begins as a nebula, spends much of its life as a main-sequence star, and then becomes a red giant, a planetary nebula, a white dwarf, and, finally, a black dwarf.

Stellar Remnants White dwarfSmall size (some no larger than Earth)DenseCan be more massive than the SunSpoonful weighs several tonsAtoms take up less space Electrons displaced inwardCalled degenerate matter Hot surfaceCools to become a black dwarf

White DwarfsDegenerate stellar remnant (C,O core)Extremely dense: 1 teaspoon of WD material: mass 16 tons!!!White Dwarfs:Mass ~ MsunTemp. ~ 25,000 KLuminosity ~ 0.01 LsunChunk of WD material the size of a beach ball would outweigh an ocean liner!

White Dwarfs (2)Low luminosity; high temperature => White dwarfs are found in the lower left corner of the Hertzsprung-Russell diagram.

Stellar Remnants Neutron Stars A neutron star is a star of extremely high density composed entirely of neutrons. (Electrons combine with protons to produce neutrons.) Neutron stars are thought to be remnants of supernova events. A teaspoonful of neutron star weigh about 100 million metric tons in Earths gravity Neutron stars are even smaller and denser than white dwarfs. May contain as much as 3x the mass of the Sun but be only about 20 km in diameter, the size of a large asteroid or a town on Earth.

Stellar Remnants Supernovae A pulsar is a source that radiates short bursts or pulses of radio energy in very regular periods. A pulsar found in the Crab Nebula during the 1970s is undoubtedly the remains of the supernova of 1054. A pulsars short for pulsating radio sources are neutron stars. In 1967, a British astronomy student Jocelyn Bell detected an object in space which give off regular pulses of radio waves and later concluded as neutron star.

The Famous Supernova of 1987: SN 1987ABeforeAt maximumUnusual type II Supernova in the Large Magellanic Cloud in Feb. 1987

Supernova RemnantsThe Cygnus LoopThe Veil NebulaThe Crab Nebula: Remnant of a supernova observed in a.d. 1054Cassiopeia AOpticalX-rays

Stellar Remnants Black Holes A black hole is a massive star that has collapsed to such a small volume that its gravity prevents the escape of everything, including light.

Scientists think that as matter is pulled into a black hole, it should become very hot and emit a flood of X-rays before being pulled in.

Stellar Remnants Black hole More dense than a neutron starIntense surface gravity lets no light escapeAs matter is pulled into itBecomes very hotEmits x-raysLikely candidate is Cygnus X-1, a strong x-ray source

Black HoleNo light can escape a black hole=> Black holes can not be observed directly.

Black Hole=> Strong X-ray source!Matter gets pulled off from the companion star, forming an accretion disk. Heats up to a few million K. Mass > 3 Msun=> Black hole!

Summary of Evolution for Stars of Various Masses

KESIMPULAN-KEMATIAN BINTANG Apabila semua gas hidrogen di teras bintang telah habis digunakan, teras itu akan mengecut. Pengecutan ini membebaskan banyak haba lalu memanaskan lapisan luar bintang. Lapisan luar yang masih kaya dengan gas hidrogen itu akan terbakar. Hal ini menyebabkan bintang mengembang dengan hebatnya serta bersinar dengan warna merah menjadi bintang raksasa merah. Raksasa merah mempunyai diameter yang boleh mencapai 100 kali diameter Matahari. Peringkat ini menandakan bintang sudah hampir ke akhir hayat. Contoh bintang raksasa merah ialah bintang Arcturus Kematian bintang (1-3) X Sun medium-mass star

KEMATIAN BINTANG Perubahan berikut akan berlaku: (a) Lapisan luarnya akan tersebar jauh ke angkasa lepas secara perlahan-lahan, mengembang menjadi raksasa merah meninggalkan teras bintang. Teras bintang akan mengecut menjadi planetary nebula dan seterusnya menjadi kerdil putih (b) Kerdil putih ialah bintang yang kecil yang sebahagian besar terdiri daripada jisim elektron yang merosot, amat tumpat dan malap (c) Apabila kerdil putih kehabisan semua tenaganya, ia akan kelihatan gelap di angkasa dan dikenal sebagai kerdil hitam. Kematian bintang (1-3) X Sun - medium-mass star

KEMATIAN BINTANG Perubahan berikut akan berlaku: (a) Raksasa merah akan semakin mengembang sehingga menjadi sangat besar dan dikenal sebagai superraksasa merah. Superraksasa merah mungkin mempunyai diameter 400-500 kali diameter Matahari. Contoh bintang superraksasa ialah Antares dan Betelgeuse. (b) Akhirnya superraksasa merah akan meletup dengan kuat. Letupan tersebut dipanggil supernova. Semasa letupan berlaku, banyak tenaga haba dan cahaya dihasilkan. Lapisan luar bintang pula tercampak jauh ke angkasa lepas meninggalkan terasnya. Kematian bintang (Massive star ~6x Sun)

KEMATIAN BINTANG Perubahan berikut akan berlaku: (c) Teras bintang yang tertinggal akan mengecut sehingga menjadi sangat tumpat dan mempunyai daya tarikan graviti yang tinggi. (d) Jika teras bintang itu terdiri terutamanya neutron ia disebut bintang neutron. Bintang neutron amat kecil, diameternya beberapa kilometer sahaja tetapi amat tumpat (3x the mass of the Sun but be only about 20 km in diameter). Bintang ini berputar dengan cepat dan memancarkan denyutan gelombang radio. Bintang neutron juga dikenali sebagai pulsar. Ia akan menyejuk dan akhirnya lenyap. Kematian bintang (Massive star ~ 6x Sun)

KEMATIAN BINTANG Teras bintang yang tertinggal akan mengecut sehingga menjadi sangat tumpat dan mempunyai daya tarikan graviti yang tinggi.

Teras yang tertinggal itu sangat besar dan sangat tumpat ia disebut lubang hitam (lohong hitam).

Lubang hitam mempunyai daya tarikan graviti yang amat kuat sehinggakan semua objek berhampiran dengannya termasuk cahaya ditarik ke dalamnya. Hal ini menjadikan kawasan ini kelihatan hitam. Kematian bintang (Massive star ~20x Sun)

BINTANG

Tamat

Organizing the Family of Stars: The Hertzsprung-Russell DiagramWe know: Stars have different temperatures, different luminosities, and different sizes. To bring some order into that zoo of different types of stars: organize them in a diagram of LuminosityversusTemperature (or spectral type)LuminosityTemperatureSpectral type: O B A F G K MHertzsprung-Russell DiagramorAbsolute mag.0

The Hertzsprung-Russell DiagramMost stars are found along the Main Sequence0

The Hertzsprung-Russell Diagram (2)Stars spend most of their active life time on the Main Sequence (MS).Same temperature, but much brighter than Main Sequence stars0

The Radii of Stars in the H-R Diagram1,000 times the suns radius100 times the suns radiusAs large as the sunRigelBetelgeuseSunPolaris0

The Relative Sizes of Stars in the HR Diagram0

Luminosity ClassesIa Bright SupergiantsIb SupergiantsII Bright Giants III GiantsIV SubgiantsV Main-Sequence StarsIaIbIIIIIIVV0

Masses of Stars in the H-R DiagramThe more massive a star is, the brighter it is:High-mass stars have much shorter lives than low-mass stars:Sun: ~ 10 billion yr.10 Msun: ~ 30 million yr.0.1 Msun: ~ 3 trillion yr.Low massesHigh massesMassL ~ M3.5tlife ~ M-2.50

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