Astro Coffee

Suggested papers for
Tue, Jan 21, Wed, Jan 22, and Fri, Jan 24, 2020

22 Jan 2020

Search for decaying heavy dark matter in an effective interaction framework: a comparison of $γ$-ray and radio observations

We investigate and compare the possibilities of observing decaying dark matter (DM) in $\gamma$-ray and radio telescopes. The special emphasise of the study is on a scalar heavy DM particle with mass in the trans-TeV range. DM decays, consistent with existing limits on the life time, are assumed to be driven by higher dimensional effective operators. We consider both two-body decays of a scalar dark particle and a dark sector having three-body decays, producing two standard model particles. It...

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23 Jan 2020

An Eclipsing Substellar Binary in a Young Triple System discovered by SPECULOOS

Mass, radius, and age are three of the most fundamental parameters for celestial objects, enabling studies of the evolution and internal physics of stars, brown dwarfs, and planets. Brown dwarfs are hydrogen-rich objects that are unable to sustain core fusion reactions but are supported from collapse by electron degeneracy pressure. As they age, brown dwarfs cool, reducing their radius and luminosity. Young exoplanets follow a similar behaviour. Brown dwarf evolutionary models are relied upon ...

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20 Jan 2020

Could quasar lensing time delays hint to cored dark matter halos, instead of $H_0$ tension?

The time delay measured between the images of gravitationally lensed quasars probes a combination of the angular diameter distance to the source-lens system and the mass density profile of the lens. Observational campaigns to measure such systems have reported a determination of the Hubble parameter $H_0$ that shows significant tension with independent determination based on the cosmic microwave background (CMB) and large scale structure (LSS). We show that lens mass models that exhibit a core...

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21 Jan 2020

Resolving the $H_0$ tension with diffusion

The tension between the value of the Hubble constant $H_0$ determined from local supernovae data and the one inferred from the cosmic microwave background based on the $\Lambda$CDM cosmological model may indicate the need for new physics. Here, we show that this `Hubble tension' can be resolved in models involving an effective energy flux from the matter sector into dark energy resulting naturally from a combination of unimodular gravity and an energy diffusion process. The scheme is one where...

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16 Jan 2020

Gravitational waves or deconfined quarks: what causes the premature collapse of neutron stars born in short gamma-ray bursts?

We infer the collapse times of long-lived neutron stars into black holes using the X-ray afterglows of 18 short gamma-ray bursts. We then apply hierarchical inference to infer properties of the neutron star equation of state and dominant spin-down mechanism. We measure the maximum non-rotating neutron star mass $M_\mathrm{TOV} = 2.31 ^{+0.36}_{-0.21} M_{\odot}$ and constrain the fraction of remnants spinning down predominantly through gravitational-wave emission to $\eta = 0.69 ^{+0.21}_{-0.39...

21 Jan 2020

13C17O suggests gravitational instability in the HL Tau disc

We present the first detection of the 13C17O J=3-2 transition toward the HL Tau protoplanetary disc. We find significantly more gas mass (at least a factor of ten higher) than has been previously reported using C18O emission. This brings the observed total disc mass to 0.2 M, which we consider to be a conservative lower limit. Our analysis of the Toomre Q profile suggests that this brings the disc into the regime of gravitational instability. The radial region of instability (50-110 au) coinci...


Updated 2020/01/24 15:53:16