Kurzgesagt – In a Nutshell
Sources – Neutron Stars
We want to thank the following experts for their scientific support:
- Dr. Matt Caplan
Assistant Professor of Physics at Illinois State University
– Neutron stars are only a few kilometers in diameter but as massive as stars.
#NASA: Neutron Stars, 2007
https://www.nasa.gov/mission_pages/GLAST/science/neutron_stars.html
– Stars exist because the mass of millions of billions of trillions of tons of hot plasma are being pulled inwards by gravity, while fusion releases energy, which pushes against gravity.
#University of Maryland, Introductory Astronomy: Main Sequence Stars, 2018
https://www.astro.umd.edu/resources/introastro/main_seq.html
#NASA, Imagine the universe!, Introduction: Stars, 2014
https://imagine.gsfc.nasa.gov/science/objects/stars1.html
– Medium stars like our sun eventually turn into white dwarfs.
#NASA, Imagine the universe!, Introduction: White Dwarfs, 2006
https://imagine.gsfc.nasa.gov/science/objects/dwarfs1.html
– But in stars many times the mass of our sun, things get interesting when the helium is exhausted.
It is important to note that not all massive stars follow the same evolutionary path. Though the nuclear burning proceeds in much the same sequence, the effect they have on the star’s hydrostatic equilibrium depends sensitively on the stars mass (see for example Figure 2.1 in Lisakov 2018 below). The exact sequence and extent of radial growth, mass loss, and core contraction, and the number of these phases will be largely determined by the initial mass of the star and the stellar models used to calculate their evolution. The video describes roughly what happens without exactly following the evolutionary sequence of any one supernova progenitor.
– M. Caplan personal communication
#Lisakov 2018, Core-collapse supernovae and their progenitors, 2018
https://tel.archives-ouvertes.fr/tel-02018238/document
#Core-Collapse, retrieved 2019
http://astronomy.swin.edu.au/cosmos/c/core-collapse
– Iron is nuclear ash, it has no energy to give and cannot be fused.
#Max Planck Institute, Cosmic Crashes Forging Gold, 2011
#Nuclear Binding Energy, retrieved, 2019
http://hyperphysics.phy-astr.gsu.edu/hbase/NucEne/nucbin.html
– An iron ball the size of the earth is squeezed into a ball of pure nuclear matter the size of a city.
#NASA: Neutron Stars, 2007
https://www.nasa.gov/mission_pages/GLAST/science/neutron_stars.html
#Max Planck Institute, retrieved 2019
https://www.mpa-garching.mpg.de/84444/Physics-and-Neutrino-Physics-Around-Hot-Neutron-Stars
– But not just the core, the whole star implodes, gravity pulling the outer layers in at 25% the speed of light. This is what we call a supernova.
Matter infalling onto a proto-neutron star in a core collapse supernova is falling in at approximately the escape velocity of a neutron star - for a 1 solar mass, 12 km neutron star this is about 50% the speed of light. However, this is not exact. Not all proto-neutron stars have the same mass and they have not finished contracting, and the infalling matter is turbulent and not necessarily spherically symmetric. Nevertheless, infall velocities are guaranteed to be a fraction of the speed of light.
– M. Caplan personal communication
#Wolfram Alpha, 2019
https://www.wolframalpha.com/input/?i=sqrt%282*G*+1+solar+mass+%2F+12+km%29+%2Fc
#Supernova Lecture Notes, Prof. R. Pogge, Ohio State University Astronomy, 2006
http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit3/supernova.html
#Research Interest - Neutron Stars, 2019
https://www.mpifr-bonn.mpg.de/research/fundamental/neutronstars
– Its mass is around a million times the mass of the Earth, but compressed to an object about 25 kilometers wide!
Observed neutron star masses vary between approximately 1 and 2 solar masses, with the most massive known at the time of writing being 2.1 solar masses (Cromartie et al 2019), greater than 700,000 Earth masses. Upper limits may be taken to be greater than this but are now generally taken to be less than 3 solar masses, equivalent to approximately 1 million earth masses.
– M. Caplan personal communication
#Cromartie et al, Nature Astronomy, 2019
https://www.nature.com/articles/s41550-019-0880-2
– That’s roughly a billion tons, in a space the size of a sugar cube.
#NASA: Neutron Stars, 2007
https://www.nasa.gov/mission_pages/GLAST/science/neutron_stars.html
– A neutron star is unbelievably extreme. Its gravity is the strongest outside black holes.
#Universe Today: Neutron Stars have Crusts of Super Steel, 2009
https://www.universetoday.com/30526/neutrons-stars-have-crusts-of-super-steel/
– Light is bent around it, meaning you can see the front and parts of the back.
#Space: Neutron Stars. Definition & Facts, 2018
https://www.space.com/22180-neutron-stars.html
– Their surfaces reach a million degrees Celsius, compared to a measly 6000° for our sun.
#ESA: XMM-Newton sees hot spots on neutron stars, 2005
https://www.esa.int/ESA_Multimedia/Images/2005/04/XMM-Newton_sees_hot_spots_on_neutron_stars
– Neutron stars in many ways are also like planets, with solid crusts over a liquid core.
#Neutron Star Suffers a “Glitch”, Gives Astronomers a Glimpse Into How They Work
, 2019
– The crust is extremely hard. The outermost layers are made of iron leftover.
#Physics of Neutron Star Crusts, 2008
https://link.springer.com/article/10.12942/lrr-2008-10
– Protons and neutrons rearrange, making long cylinders or sheets, which physicists call ‘nuclear pasta. Lumps of pasta inside a neutron star can even make mountains, at most a few centimeters high, but many times as massive as the Himalayas.
#The Elasticity of Nuclear Pasta, 2018
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.132701
– We’re not really sure what the properties of matter in the core are. Protons and neutrons might dissolve into an ocean of a so called ‘quark gluon plasma.
#Jha, From nuclear matter to Neutron Stars, 2009
https://arxiv.org/pdf/0902.0262.pdf
Fig 2 in particular for a schematic illustration
#Maximum mass of neutron stars with a quark core, 2002
https://www.sciencedirect.com/science/article/pii/S0370269301014794
– Some of those quarks might turn into ‘strange quarks,’ making a sort of ‘strange matter’.
We already did a video on quark stars and strange matter. If you are interested, check it out here:
The video:
https://www.youtube.com/watch?v=p_8yK2kmxoo
The sources:
https://sites.google.com/view/sourcesquarkstars
#Strange matter in compact stars, 2017
https://arxiv.org/pdf/1711.11260.pdf
#Jha, From nuclear matter to Neutron Stars, 2009
https://arxiv.org/pdf/0902.0262.pdf
– When neutron stars first collapse, they begin to spin very very fast.
#A Radio Pulsar Spinning at 716 Hz, 2006
https://science.sciencemag.org/content/311/5769/1901
– These radio pulsars are the best known type of neutron star, about 2,000 are known in the Milky Way.
#A magnetar at the heart of our Milky Way, 2013
https://www.mpg.de/7502957/magnetar_milkyway
#What Are Pulsars?, 2016
https://www.space.com/32661-pulsars.html
– These magnetic fields are the strongest in the universe, a quadrillion times stronger than earth’s after they are born.
#A New Signal for a Neutron Star Collision Discovered, 2019
– Neutron stars can can crash into and kill each other.
#When Neutron Stars Collide: Scientists Spot Kilonova Explosion from Epic 2016 Crash, 2019
https://www.space.com/colliding-neutron-stars-caued-massive-kilonova-explosion.html
– Only very recently we learned that this is probably the origin of most of the heavy elements in the universe, like gold, uranium and platinum and dozens more.
#Identification of strontium in the merger of two neutron stars, 2019
– So then, our two neutron stars collapse and become a black hole, dying yet again.
#When will a neutron star collapse to a black hole?, 2016
https://phys.org/news/2016-04-neutron-star-collapse-black-hole.html