![Variable Star Astronomy
Variable stars are stars whose brightness changes because of physical changes within the star. There exist more than 30,000 variable stars in just the Milky Way. Variable star astronomy is a popular part of astronomy because amateur astronomers play a key role. They have submitted thousands of observed data and these data are logged onto a database. American readers can find information on it on the American Association of Variable Star Observers page.
One of such variable stars are called Cepheids. Cepheids are pulsating variable stars because they undergo a “repetitive expansion and contraction of their outer layers” [1]. In Cepheids, the star’s period of variation (about 1-70 days) is related to its luminosity; the longer the period, the higher the luminosity. In fact, when graphed, the relationship is shown by a straight line (as can be seen on the title image). Henrietta Swan Leavitt, an American astronomer, first discovered this and understood the significance of this knowledge. Combined with understanding of the star’s apparent magnitude (a previously written post on this subject can be found here), astronomers can use this information to find a star’s distance from Earth. Cepheids are famously known for their usefulness in finding distances to far-away galaxies and other deep sky objects. Leavitt died early from cancer but was to be nominated for the Nobel Prize in Physics by Professor Mittag-Leffler (Swedish Academy of Sciences).
Edwin Hubble used Leavitt’s discovery to prove that the Andromeda Galaxy (M31) is not part of the Milky Way, but was able to find the distance to the Andromeda Galaxy (between 2-9 million light years away). At first his calculation was incorrect (900,000 light years) because he observed Type I (classical) Cepheid Stars. Type I Cepheid stars are brighter, newer Population I stars. Hubble later used type II Cepheids (also called W Virginis stars), which are smaller, dimmer, Population II stars, and he was able to make more accurate calculations.
To determine the star’s distance, use the inverse square law of light brightness.
A similar type of star are RR Lyrae Variable Stars. They are smaller than Cepheids and have a much shorter period (from a few hours to a day). On the other hand, they are far more common. Likewise, they can be used to solve for distances as well. Low mass stars live longer, and thus Cepheid stars are generally younger because they are more massive.
Both Cepheids and RR Lyrae Variable stars are referred to as standard candles: objects with known luminosity. If you’ve ever wondered how astronomers came to those enormous figures when describing how far away galaxies and stars are from us, you can now better understand why and how.](http://25.media.tumblr.com/tumblr_luo93515tH1qmyxvuo1_500.gif)
Variable Star Astronomy
Variable stars are stars whose brightness changes because of physical changes within the star. There exist more than 30,000 variable stars in just the Milky Way. Variable star astronomy is a popular part of astronomy because amateur astronomers play a key role. They have submitted thousands of observed data and these data are logged onto a database. American readers can find information on it on the American Association of Variable Star Observers page.
One of such variable stars are called Cepheids. Cepheids are pulsating variable stars because they undergo a “repetitive expansion and contraction of their outer layers” [1]. In Cepheids, the star’s period of variation (about 1-70 days) is related to its luminosity; the longer the period, the higher the luminosity. In fact, when graphed, the relationship is shown by a straight line (as can be seen on the title image). Henrietta Swan Leavitt, an American astronomer, first discovered this and understood the significance of this knowledge. Combined with understanding of the star’s apparent magnitude (a previously written post on this subject can be found here), astronomers can use this information to find a star’s distance from Earth. Cepheids are famously known for their usefulness in finding distances to far-away galaxies and other deep sky objects. Leavitt died early from cancer but was to be nominated for the Nobel Prize in Physics by Professor Mittag-Leffler (Swedish Academy of Sciences).
Edwin Hubble used Leavitt’s discovery to prove that the Andromeda Galaxy (M31) is not part of the Milky Way, but was able to find the distance to the Andromeda Galaxy (between 2-9 million light years away). At first his calculation was incorrect (900,000 light years) because he observed Type I (classical) Cepheid Stars. Type I Cepheid stars are brighter, newer Population I stars. Hubble later used type II Cepheids (also called W Virginis stars), which are smaller, dimmer, Population II stars, and he was able to make more accurate calculations.
To determine the star’s distance, use the inverse square law of light brightness.
A similar type of star are RR Lyrae Variable Stars. They are smaller than Cepheids and have a much shorter period (from a few hours to a day). On the other hand, they are far more common. Likewise, they can be used to solve for distances as well. Low mass stars live longer, and thus Cepheid stars are generally younger because they are more massive.
Both Cepheids and RR Lyrae Variable stars are referred to as standard candles: objects with known luminosity. If you’ve ever wondered how astronomers came to those enormous figures when describing how far away galaxies and stars are from us, you can now better understand why and how.
The Neutron Star
When a star runs out of fuel it eventually goes through a gravitational collapse. There are several possible outcomes, and three come about by simply taking into account only the mass of the star that has just collapsed. If the star is less than 1.5 solar masses, then a white dwarf is formed. Yet if its mass is larger than 5 solar masses, it will create a black hole. What about if the star’s mass was in between those two points? Well, that’s when a neutron star is formed. Due to the inward collapse of such a star, electrons combine with protons to form neutrons – thus giving the resultant celestial body the name “neutron star”.
Neutron stars characteristically have extremely high densities. Anything falling into a neutron star is super-accelerated by gravity (which is 100 billion times stronger than what we experience on earth). “If you dropped a marshmallow onto a neutron star, it would have the energy of an atomic bomb,” says Chip Meegan from the Marshal Space Flight Center of NASA. Neutron stars also have insanely strong magnetic fields, approximately 2 x 1011 times those of Earth. These stars are usually very hot. The degeneracy pressure due to the Pauli exclusion principle (no two neutrons or any other fermions can occupy the same place and quantum state simultaneously) ensures the neutron star’s stability and prevents it from collapse. (The only situation in which a neutron star would collapse into a black hole is if it is gradually absorbing matter from an accompanying binary star.)
Pulsars!
Very simply, pulsars are rotating neutron stars. Because they conserve the angular momentum of the stars from which they were formed, pulsars can spin at rates over 700 times revolutions per second. They stream jets of highly energetic particles (which have speeds close to that of light) out from their magnetic poles, producing extremely powerful beams of radiation. This combined with their rotational movement allows them to appear as if they are pulsing when they are observed. The rotational and magnetic axes of these stars are misaligned, which causes the beam of light from the jets to “sweep” around as the pulsar rotates, giving rise to the lighthouse effect.
The H-R Diagram
- named after Danish and American astronomers Ejnar Hertzsprung and Henry Russel
- a graphical representation of the relationship between the luminosity, surface temperature, and radius of stars
- it is known to be the most important diagram in astronomy as it shows the state of a star throughout its life
![Absolute Magnitude of a Star
Out of all the stars that we observe at night, it is easy to identify a certain few. Is it because they look brighter to us?
As observers on earth, we only notice the apparent magnitude (m) of the star.
Astronomers often need to know how much light a star truly radiates into space. This is referred to as the star’s luminosity.The stars we see in the sky are oftentimes different distances away from us.
Let’s imagine 2 stars which look equally bright to us. The further star has a greater luminosity, a greater absolute magnitude (M). The absolute magnitude of a star is the apparent magnitude that it would have if it were observed at a distance of 10 parsecs.
To fairly compare stars at different distances, scientists use the absolute magnitude formula:
M = m-5log(d/10)
Where:
M= absolute magnitude
m= apparent magnitude
d= distance in parsecs*
*Note: A parsec is equivalent to 3.26 light years
Image is Star Cluster NGC 1850. [Image source]](http://24.media.tumblr.com/tumblr_lo6z3wdb8b1qmyxvuo1_400.jpg)
Absolute Magnitude of a Star
Out of all the stars that we observe at night, it is easy to identify a certain few. Is it because they look brighter to us?
As observers on earth, we only notice the apparent magnitude (m) of the star.
Astronomers often need to know how much light a star truly radiates into space. This is referred to as the star’s luminosity.The stars we see in the sky are oftentimes different distances away from us.
Let’s imagine 2 stars which look equally bright to us. The further star has a greater luminosity, a greater absolute magnitude (M). The absolute magnitude of a star is the apparent magnitude that it would have if it were observed at a distance of 10 parsecs.
To fairly compare stars at different distances, scientists use the absolute magnitude formula:
M = m-5log(d/10)
Where:
M= absolute magnitude
m= apparent magnitude
d= distance in parsecs*
*Note: A parsec is equivalent to 3.26 light years
Image is Star Cluster NGC 1850. [Image source]
