Materials scientist Suveen Mathaudhu has refuted astrophysicist Neil deGrasse Tyson's claim that Thor's hammer weights more than 300 billion elephants.
Technically, Neil deGrasse Tyson wasn't incorrect when he tweeted earlier this month:
If Thor's hammer is made of neutron-star matter, implied by legend, then it weighs as much as a herd of 300-billion elephants— Neil deGrasse Tyson (@neiltyson) February 5, 2013
He did say if. However, Mjolnir, the hammer wielded by Marvel's Thor, is not made of neutron star, as program manager in the materials science division of the US Army Research Office Suveen Mathaudhu pointed out.
"The critical mistake Tyson makes is thinking that Mjolnir was forged of the core of a dying star, when it was actually forged in the core of a dying star," he told the NC State University's The Abstract.
In fact, as Mathaudhu explained, according to official Marvel lore, the hammer is actually made of an Asgardian metal called Uru, and a trading card states that it weighs 19.187 kilograms — according to Mathaudhu, it would have a density of about 2.13 grams per cubic centimetre, lighter than aluminium.
The clue to its "heaviness" lays in the inscription on the hammer's head: "Whosoever holds this hammer, if he be worthy, shall possess the power of Thor". Only a worthy bearer is able to lift Mjolnir.
Thankfully, because Uru is fictional, it can possess that kind of lightness quite easily. However, Mathaudhu posits a theory about what the metal could possibly be in the real world:
Perhaps Uru is the "holy grail" of high-pressure physics: a form of metallic hydrogen. Some predictions of the density of metallic hydrogen fall into this range; it requires extreme conditions to form and could be a tremendous energy source. It's thought to be present at the core of planets, such as Jupiter, and at the core of suns — which are stars, after all.
Just not dying ones.