HST discovers Cepheid variables in M100

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Hubble discovers Cepheid variables in M100

The Grand Design Spiral Galaxy M100

[M100 Color Image]

Hubble Space Telescope image of the grand design of spiral galaxy M100

taken on December 31, 1993 with the Wide Field Planetary Camera 2 (WFPC 2).

This color picture is a composite of several images taken in different colors

of light. Blue corresponds to regions containing hot newborn stars.

Hubble, for the first time, could resolve individual stars within the majestic

spiral arms; these stars typically appeared blurred together when viewed with

ground-based telescopes.

Hubble has measured accurately the light from the very faint stars in M100,

and has identified about 20 Cepheid Variable stars embedded within M100’s

spiral arms. From the measurements of their pulsation period, the intrinsic

brightness of these stars can be determined. As the apparent brightness is

acurately measured also, one can calculate how distant the stars must be

to appear at the observed magnitude, which gives a considerably precise

value for the galaxy’s distance: M100 is about 56 million light years distant.

M100 is a majestic face-on spiral galaxy. It is a rotating system of gas and

stars, similar to our own galaxy, the Milky Way. Hubble routinely can view

M100 with a level of clarity and sensitivity previously possible only for the

Local Group galaxies.

[Full original image caption]


Cepheid Variable Star in M100

[Cepheids in M100, A]

This NASA HST image of a region of the galaxy M100, taken in the visible

light, shows the representative of a class of pulsating star called a Cepheid

Variable. Though rare, these stars are reliable distance indicators to

galaxies. Based on the Hubble observation, the distance to M100 has been

measured accurately as 56 million light-years (+/- 6 million light-years),

making it the farthest object where intergalactic distances have been

determined precisely.

Hubble’s high resolution pinpoints a Cepheid, which is located in a

starbirth region in one of the galaxy’s spiral arms (bottom frame). The top

three frames were taken on (from left to right) May 9, May 4, May 31, and

they reveal that the star (in center of each box) changes brightness.

Cepheids go through these changes rhythmically over a few weeks. The

interval it takes for the Cepheid to complete one pulsation is a direct

indication of the stars’s intrinsic brightness. This value can be used to

make a precise measurement of the galaxy’s distance.

[Full original image caption]


Hubble Snapshots Capture Pulsation Rate of a “Stellar Milepost”

[Cepheids in M100, B]

This sequence of images taken with NASA’s Hubble Space Telescope

chronicles the rhythmic changes in a rare class of variable star (located in

the center of each image) in the spiral galaxy M100. The images were taken

in the visible light in 1994. This class of

pulsating star is called a Cepheid Variable. The Cepheid in this Hubble

picture doubles in brightness (24.5 to 25.3 apparent magnitude) over a

period of 51.3 days.

The interval it takes for the Cepheid to complete one pulsation is a direct

indication of the stars’s intrinsic brightness. This value can be used to

make a precise measurement of the galaxy’s distance, which turns out to be

56 million light-years from Earth.

[Full original image caption]


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