Triangulum Log - Post 3 - The Vista System

What are white dwarfs?

Some curiosities about white dwarfs, a stellar corpse and the future of the sun.

Where a star ends up at the end of its life depends on the mass it was born with. Stars that have a lot of mass may end their lives as black holes or neutron stars.

A white dwarf is what stars like the Sun become after they have exhausted their nuclear fuel. Near the end of its nuclear burning stage, this type of star expels most of its outer material, creating a planetary nebula.

In 5.4 billion years from now, the Sun will enter what is known as the Red Giant phase of its evolution. This will begin once all hydrogen is exhausted in the core and the inert helium ash that has built up there becomes unstable and collapses under its own weight. This will cause the core to heat up and get denser, causing the Sun to grow in size.

It is calculated that the expanding Sun will grow large enough to encompass the orbit’s of Mercury, Venus, and maybe even Earth.

A typical white dwarf is about as massive as the Sun, yet only slightly bigger than the Earth. This makes white dwarfs one of the densest forms of matter, surpassed only by neutron stars and black holes.

The gravity on the surface of a white dwarf is 350,000 times that of gravity on Earth. 

White dwarfs reach this incredible density because they are so collapsed that their electrons are smashed together, forming what is called “degenerate matter.” This means that a more massive white dwarf has a smaller radius than its less massive counterpart. Burning stars balance the inward push of gravity with the outward push from fusion, but in a white dwarf, electrons must squeeze tightly together to create that outward-pressing force. As such, having shed much of its mass during the red giant phase, no white dwarf can exceed 1.4 times the mass of the sun.

While many white dwarfs fade away into relative obscurity, eventually radiating away all of their energy and becoming a black dwarf, those that have companions may suffer a different fate.

If the white dwarf is part of a binary system, it may be able to pull material from its companion onto its surface. Increasing the mass can have some interesting results.

One possibility is that adding more mass to the white dwarf could cause it to collapse into a much denser neutron star.

A far more explosive result is the Type 1a supernova. As the white dwarf pulls material from a companion star, the temperature increases, eventually triggering a runaway reaction that detonates in a violent supernova that destroys the white dwarf. This process is known as a single-degenerate model of a Type 1a supernova. 

If the companion is another white dwarf instead of an active star, the two stellar corpses merge together to kick off the fireworks. This process is known as a double-degenerate model of a Type 1a supernova.

At other times, the white dwarf may pull just enough material from its companion to briefly ignite in a nova, a far smaller explosion. Because the white dwarf remains intact, it can repeat the process several times when it reaches the critical point, briefly breathing life back into the dying star over and over again. 

Image credit: www.aoi.com.au, NASA, Wikimedia Commons, Fsgregs, quora.com, quora.com, NASA’s Goddard Space Flight Center, S. Wiessinger, ESO, ESO, Chandra X-ray Observatory

Source: NASA, NASA, space.com

Picture of the day - February 15, 2019

Gas giant with vivid violet rings.

Picture of the day - November 16, 2018

An Earth-Moon analog.

Pictures of the Day - December 15, 2018

Insight A System - Second Planet (Insight A-II)

Insight A-II is the second planet orbiting Insight A. It is a Venus-like planet shrouded in a thick carbon dioxide and water vapor atmosphere 716 times thicker than Earth’s. The surface temperature averages 1,980 F, and most of the surface is covered in molten rock.

The planet orbits just 0.07 AU from the sun, completing an orbit once every 6.72 Earth days. Insight A-II is a super-earth with a mass 2.66 times that of Earth and a radius of 1.15 Earths.

High Resolution Pictures

Insight A-II

Comet-like planet

The Atmosphere

The Surface

Picture of the day - January 23, 2019

Galaxy looms large behind the rings of a gas giant.

Picture of the Day 2 - January 23, 2019

A hazy moon begins to hide behind the shadow of a gas giant.

Second one since I missed a day.

Lunar Silhouettes

Picture of the Day - October 22, 2018

Another gas-giant and its moons. Here the atmosphere of the gas giant and its inner moon glow against the dark background, illuminated by scattered light, viewed from just above the atmosphere of a second satellite.

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Alien Planet View

Gas Giant Eclipse

Picture of the Day - October 13, 2018

The sky of a large moon orbiting a gas giant right before an eclipse.