Say It With Science

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.

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]

Gravitation

What is Gravity? The stuff that keeps our feet glued to the earth, the stuff that hit Isaac Newton’s head with an apple, the stuff that keeps our Earth revolving around the sun?

Isaac Newton’s Universal Law of Gravitation states that “Every particle in the universe attracts every other particle with a force along a line joining them. The force is directly proportional to the product of their masses and inversely proportional to the square of the distance between them”. ‘

Gravity seems to be very simple in definition, in that it “is always attractive, and it depends only on the masses involved and the distances between them”. 

The Newtonian definition of gravity seemed to fit most-Earthly situations. But when you account for massive, stellar objects, Newton could not properly explain their properties! For instance, the Newtonian definition could not explain Mercury’s distorted orbit around the sun. 

Albert Einstein’s Theory of General Relativity accounts for these situations with ease, though! General Relativity proposes that all of space and time is composed in a fabric-like structure. Stellar objects are suspended in this fabric. As any Earthly being knows— a dense object (such as a tennis ball) laid on a cotton sheet will cause the sheet to sink and form a dent. 

If you place say, an M&M or a small candy in that sheet, the candy piece will be drawn to the dent and will sink! Say that cotton fabric was actually really long and wide. If you place the M&M on the edge of the sheet, away from the tennis ball, it could probably sustain itself. 

Einstein applied this concept to the Universal fabric of space-time. Space-time is 4 dimensional, so it is not only space that is warped. 

General Relativity has been experimentally accurate. It is the most current and up-to-date knowledge on the nature of space and time. The hunt has not ended, though. With the recent progress scientists have made, quantum mechanics proposes theory on forces at the subatomic level.

The electromagnetic, strong, and weak forces can be explained on the quantum level. Gravity, though, remains excluded. Modern physics aims to unify the four forces of nature. General Relativity must fit in the picture of Quantum Mechanics! This is a search for the “theory of everything”. 

The quest for Quantum Gravity is a relatively new, unique field of research. One hope lies in String Theory. 

It is exciting to notice how even an ordinary question, “Why does the apple fall on my head?” has far more depth behind it. The question has lead scientists to venture into new fields of study for more than decades.