1 / 9

STANDARD CANDLES

An important aspect of the work of astronomers is to determine the distance of stars and galaxies from Earth. <br>

LARANYA
Download Presentation

STANDARD CANDLES

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ASTRONOMY AND COSMOLOGY

  2. Standard candle • An important aspect of the work of astronomers is to determine the distance of stars and galaxies from Earth. • A galaxy is a group of hundreds of millions of stars, stellar remnants, gas and dark matter, held together by gravity. • Galaxies are so far from Earth that, to the naked eye, they appear either as a small speck of light or cannot be seen at all

  3. What is standard candle? To measure distance, the radiant flux intensity on Earth (observed brightness) is measured. If the actual luminosity L of the star or galaxy can be found, then the distance can be calculated using the expression F = L/(4πd2). The difficulty is in the determination of the luminosity. One way in which this problem is overcome is the use of stars known as CEPHEID VARIABLES

  4. CEPHEID VARIABLES • A Cepheid variable star is a star whose radius varies periodically. The varying radius of the star causes the temperature of the star to change and consequently, the luminosity varies periodically. The period of this variation of luminosity (and also the star’s brightness observed from Earth) ranges from 1 day to 100 days. • Cepheid variable stars were first identified by Henrietta Swan Leavitt in 1908. Leavitt also discovered that more luminous Cepheids had longer periods, and other astronomers extended her work to show that there is a relationship between the period of the star’s variation and its luminosity (see Figure 25.3)

  5. Since all Cepheids of a given period have the same luminosity, a Cepheid’s luminosity L can be estimated from the period of the variation of brightness. Hence the distance to the star is found after measuring F Using this technique, distances to Cepheid variables of up to 13 million light-years can be determined with Earth-bound telescopes. With space-bound telescopes, distances to Cepheid variables even further away can be determined. A Cepheid variable in a galaxy in the Virgo cluster was found to be 56 million light-years distant. Note that a light-year (ly) is the distance that a photon of light travels through space in one year i.e. 9.46 × 1015m: 1.0ly = 3.0 × 108 × 365 × 24 × 60 × 60 = 9.46 × 1015m

  6. Worked Example The luminosity L of a Cepheid variable is estimated from its period to be 4.6 × 10^15 W. Its radiant flux intensity (observed brightness) F measured on Earth is 1.3 × 10^−23 Wm^−2. Determine the distance of the Cepheid variable from Earth. Answer

  7. /

  8. Other standard candles Cepheid variables method does not work for galaxies that are a very long distance from Earth. Early observations were limited to Cepheid variables and to galaxies relatively close to our own galaxy. Other standard candles, such as some SUPERNOVAE may be used for more distant galaxies.

  9. Type 1A supernovae Type 1A supernovae stars implode rapidly towards the end of their lives, and scatter matter and energy out into space. This implosion event can be brighter than the galaxy itself. The luminosity of the star at the time of the implosion is always the same. From this, astronomers can estimate the star’s distance from the Earth

More Related