# Gravity and Supernova - My understanding

## Main Question or Discussion Point

My understanding of Gravity

Gravity is a force which is acting on all celestial bodies and exerting pressure on them from all directions (Ex.1 Like water exerts pressure on a submarine when dives)

Stars when loose their fuel can't withstand this force and shrink and shrink where they can't shrink anymore and result in a supernova (assuming a star is big enough)

If the size of the star is reducing because it losing mass, the relative gravity being applied on it should also decrease, but it rather increases (or so i assume) and causes a supernova.

There are some conceptual differences in my understanding. Kindly clarify me.

I will follow up with more questions once I start getting explanations.

Thank you

## Answers and Replies

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PAllen
2019 Award
phyzguy
My understanding of Gravity

Gravity is a force which is acting on all celestial bodies and exerting pressure on them from all directions (Ex.1 Like water exerts pressure on a submarine when dives)
Let's get the first part right first.

(1) Gravity acts on ALL masses, not just celestial bodies. It is acting on you as you sit in your chair.
(2) Gravity exerts a force, not a pressure. A pressure is a force/area. The amount of force is given by Newton's law of universal gravitation (look it up).
(3) The force is NOT exerted "from all directions", it is in a specific direction given by the vector sum of all the bodies acting on the mass in question.

Staff Emeritus
2019 Award
In general, "correct me where I am wrong" threads tend not to do very well. Particularly if and when the wrong ideas get defended by the OP. It is much better to ask questions as questions.

Hello Einsteinll,

Let me first answer your query in the following way. But, before that let me ask you one specific question: Are you

willing to know the relationship between gravity and supernova or how gravity is responsible for supernova?

Well here is my answer:

Gravity:

Gravity till Newton is known to be a force, as rightly told by 'phyzguy' -- it acts on all masses. Gravity before the advent of General relativity was considered as a force, then now it is visualized as a geometry of spacetime. Gravity acts on all masses.

What is a supernova?

A "nova" is a nuclear explosion in a white dwarf star (when a star dies,there are 3 possible outcomes, 1.A neutron star, 2. A white dwarf 3.A black hole).A supernova is a stellar explosion that is more energetic than a nova. "Nova" is Latin meaning -- "new." Super distinguished from ordinary nova which is less luminous.

How a supernova is formed?

Stage 1: Creation of a star: A star starts off as a ball, mostly hydrogen, that is compacted in a very dense region supported by its' own gravity. A star burns, just like a gas burns and after some time looses its fuel. As it goes on burning. the hydrogen atom starts colliding with each other to form Helium. This is called 'fusion'. Fusion causes release of a huge amount of energy and the star glows as we see. The pressure of gravity which compresses & the internal nuclear reactions are BALANCED, which keeps the star glowing.

Stage 2: Collapse:As Helium is more dense than H2, it starts settling at the star's core. Over a period of time, when there is no more Hydrogen left to burn, helium settles at the core.

Stage 3: Star Collapse and Red Giant: The pressure at temperature at the core increases until the helium atom collides to form Carbon. The intense radiation from the star's core puffs up the outer layers of the star giving off a much MORE SURFACE AREA. it increases more energy and becomes a red giant.

When it runs out of carbon, it compresses using fusion, neon -> oxygen, O2 ->H2-> helium.

This process continues forming layers until is reaches iron.

Due to atomic structure, iron (Fe) has a nucleus more stable. The star's core fill up with Fe and the star implode. Mechanically, speaking, implosion is a process, when the object is destroyed by collapsing on themselves, the exact opposite is explosion. Once, the star looses the balancing factor, implosion, gravitational collapse occurs when the stable body collapses within itself.

Implosion is a way to explosion: As the billions of tons of matter come rushing together, everything breaks. Faster than the blink of an eye, the collapse rebounds it and becomes a tremendous explosion -- SUPERNOVA.

Examples: The crab nebula was a star once. It exploded as a supernova (SN) in 1054 & it was so bright that it was visible in the day light for 23 long days !!

The Kepler SN, SN1604, was observed in 1604, happening 23,000 light years distant

Hope I could make things clear and answer your query. I have tried to give a subtle relationship between gravity and supernova.

If you have anything more, please let me know.

Thanks

mfb
Mentor
A star burns, just like a gas burns and after some time looses its fuel. As it goes on burning. the hydrogen atom starts colliding with each other to form Helium. This is called 'fusion'.
Fusion and "burning" both mean the same thing, where fusion is the proper technical term.
The pressure of gravity which compresses & the internal nuclear reactions are BALANCED, which keeps the star glowing.
The balance is between gravity and pressure from radiation and matter. Fusion is "just" required to keep the star hot.

Stage 2: Collapse:As Helium is more dense than H2, it starts settling at the star's core. Over a period of time, when there is no more Hydrogen left to burn, helium settles at the core.
The mass of helium is not really relevant here. Helium accumulates in the core because fusion happens in the core and not in the outer regions. It is as simple as that.

When it runs out of carbon, it compresses using fusion, neon -> oxygen, O2 ->H2-> helium.
At those temperatures, there are no molecules, there is no O2 or H2. What does the hydrogen do here?

davenn
Gold Member
2019 Award
What is a supernova?

A "nova" is a nuclear explosion in a white dwarf star (when a star dies,there are 3 possible outcomes, 1.A neutron star, 2. A white dwarf 3.A black hole).A supernova is a stellar explosion that is more energetic than a nova. "Nova" is Latin meaning -- "new." Super distinguished from ordinary nova which is less luminous.
The processes of a supernova and nova are quite different. A nova ISNT just a small scale supernova.
Nova stars have recurrent outbursts in brightness. Nova stars are part of a binary star system and are drawing material from its companion.

Supernovas are the result of stellar collapses and are a one off occurrence for any given star

Examples: The crab nebula was a star once. It exploded as a supernova (SN) in 1054 & it was so bright that it was visible in the day light for 23 long days !!
There is still a star there !! a millisecond pulsar - 32 times a second

cheers
Dave