Thread by @drannawatts

Thrilled that we can finally share our first NICER neutron star mass-radius results, for pulsar PSR J0030+0451. It’s been quite the ride getting to this point!!

go.nasa.gov/2LP5Pit

Before I go any further, here’s the link to papers, which are published together in an ApJ Letters Focus Issue.

iopscience.iop.org/journal/2041-8…

So what’s the bottom line?! What did we find?

NICER uses a technique called pulse profile modelling, which exploits relativistic effects on X-rays emitted from hot spots on the neutron star’s surface. And we rely on the phenomenal quality data that we get from the instrument, which sits on @ISS_Research !

@ISS_Research First and foremost - we’ve succeeded in using this new technique to measure mass and radius of a neutron star! It’s about 1.35 solar masses, and 12.7 km in radius, with uncertainties of +/- 10%. Ultimately, we’re aiming to get this to a few %!

@ISS_Research [The compactness, by the way, is much more tightly constrained, at +/- 6%.]

@ISS_Research Did we learn anything dramatic about dense nuclear matter yet? With only one measurement it’s hard to do this! But the radius is in the middle of the range predicted by nuclear theory (so the theorists can breathe easy for now!).

@ISS_Research But that’s not all we learned!

@ISS_Research One of the ‘byproducts’ of the analysis is a map of the hot X-ray emitting spots on the stellar surface. These are formed as charged particles whiz around in the star’s magnetosphere and smack into the surface, heating it up at the magnetic poles.

@ISS_Research NICER’s mission patch has a lovely image of the ‘classical’ picture of a pulsar and its magnetic field. Beautifully symmetric, with north and south magnetic poles directly opposite each other.

@ISS_Research Folks, we broke the mission patch.

@ISS_Research The hot spots are NOT opposite each other - in fact, they’re in the same hemisphere. And they are not even spots! Well, one might be - but the other seems to be a long, extended arc.

@ISS_Research To which we say:

@ISS_Research Now it’s possible to get something like this, but only if you allow a much more messy magnetic field structure, something like a quadrudipolar field (yes, this is a real word and not a typo)!

@ISS_Research But how on earth did that form? The NICER pulsars are OLD, and there are a lot of processes operating during the lives of neutron stars that you’d expect to simplify the magnetic field. But that didn’t happen. So this is a challenge for the stellar evolution folks.

@ISS_Research And let's take a moment here. We mapped the surface of a tiny star about a thousand light years from Earth. Not bad, right?

@ISS_Research I can’t begin to do justice to 7 papers in a Twitter thread, so I’m going to stop and tell you all to go read the papers, watch the movies, etc. Science always involves assumptions, caveats and so on, and the details of the analysis matter! I'm sure you'll have questions!

@ISS_Research I’ll tweet some more detailed threads in the coming days, after the papers appear on the arXiv tomorrow morning.

@ISS_Research But I want to give a shout out to the whole NICER team, especially working group leader @slavkobogdanov and the junior @uva_api scientists who led 3 of the papers - PhD students Thomas Riley and Geert Raaijmakers, and postdoc Dr Anna Bilous.

@ISS_Research @slavkobogdanov @uva_api In a piece of perfect timing, Thomas Riley (Statistical Inference Wizard and Codemaster in Chief!) defends his PhD thesis on Monday, and we could not be prouder! I’ll also note that Riley et al. smashes the record for the longest ever ApJ Letter #Squadgoals

@ISS_Research @slavkobogdanov @uva_api I also want to thank @ERC_Research for the Starting Grant that let us do this work, and @NWONieuws @SURFsara_NL for the supercomputer resources we needed. This is INTENSE work, for people and processors, and we could not have done it without the support that both provided.

@ISS_Research @slavkobogdanov @uva_api @ERC_Research @NWONieuws @SURFsara_NL [And sorry for using such a large percentage of the university’s LISA cluster allocation last year… this is why. ]

@ISS_Research @slavkobogdanov @uva_api @ERC_Research @NWONieuws @SURFsara_NL The Universe is weird and wonderful, folks. And NICER just made it that little bit weirder….

Over and out for now!!