Interpreting the spectrum of lanthanides following thegravitational waves*

In 2017, the first detection of gravitational waves due to merger of two

neutron stars was followed by a spectrum of lanthanides which has opened

up the scope for a new understanding on how heavy elements are formed.

The spectrum shows a broad feature of wavelength range of 3000 - 7000

$\AA$, and hence covering far ultraviolet (FUV) to optical (O) region.

The feature moved to infrared (IR) region during the 9 days of

observation indicating radiation absorption due to plasma opacity and

re-emission with some loss of the energy.

The current study explores to interpret the broad feature through

absorption spectroscopy of a number or lanthanides ions, Ho I-II, Er

I-IV, Tm I-V, Yb I-VI and Lu I-VII. Most of these ions produce close to

hundred thousands lines within an energy range of a few Rydberg.

Although excited only to a few orbitals up, these transitions include

X-ray lines along with those in UV, O, and IR. Number of ions are found

to fall in the energy range of the broad spectrum.