We present a multi-wavelength study of the local Leo cold cloud ( LLCC ) , a very nearby , very cold cloud in the interstellar medium .
Through stellar absorption studies we find that the LLCC is between 11.3 pc and 24.3 pc away , making it the closest known cold neutral medium cloud and well within the boundaries of the local cavity .
Observations of the cloud in the 21-cm H i line reveal that the LLCC is very cold , with temperatures ranging from 15 K to 30 K , and is best fit with a model composed of two colliding components .
The cloud has associated 100 micron thermal dust emission , pointing to a somewhat low dust-to-gas ratio of 48 \times 10 ^ { -22 } MJy sr ^ { -1 } cm ^ { 2 } .
We find that the LLCC is too far away to be generated by the collision among the nearby complex of local interstellar clouds , but that the small relative velocities indicate that the LLCC is somehow related to these clouds .
We use the LLCC to conduct a shadowing experiment in 1/4 keV X-rays , allowing us to differentiate between different possible origins for the observed soft X-ray background .
We find that a local hot bubble model alone can not account for the low-latitude soft X-ray background , but that isotropic emission from solar wind charge exchange does reproduce our data .
In a combined local hot bubble and solar wind charge exchange scenario , we rule out emission from a local hot bubble with an 1/4 keV emissivity greater than 1.1 Snowdens / pc at 3 \sigma , 4 times lower than previous estimates .
This result dramatically changes our perspective on our local interstellar medium .