HEN NEWS 05/2024 (The one with E.T. in it)

There are good news to report from the LIGO-VIRGO-KAGRA collaboration of mojor gravitational wave (GW) detectors: The universe will be given more time to thow an interesting GW event (hopefully with an optical counterpart accessible to amateurs!) at us, as the current observation run will be extended.

The new planned end-date for the "O4" run now is 9 June 2025, originally it was planned to end O4 in January 2025.

https://observing.docs.ligo.org/plan/

For a history of the observations plans and detector range estimates, you can check the git repository https://git.ligo.org/observing/plan/-/commits/main/_static/ObsScen_timeline.png?ref_type=heads

There are already plans for the next generation of detectors: In the US, the "Cosmic Explorer" concept seems to be the most promising. While the current US detectors (LIGO) feature 4 km long vacuum tunnels in an L-shape arragement to form a laser interferometer, the Cosmic Explorer concept forsees two sites with up to 40 km (!!) long vacuum systems. Note that wehn building a straight 40 km pipe, even the curvature of the Earth will add to the engineering challenges.

While there were other concepts competing with "Cosmic Explorer", an NSF report this year concluded:

Based on the materials available, we conclude that the only U.S. detector concept that can
reach the target sensitivity of ~10x better than that of the LIGO A+ design is that of Cosmic
Explorer, consisting of two possible detectors (CE40 and CE20). Considering a timeline of
~10 years focuses our attention on the first stage of Cosmic Explorer, which does not require
cryogenics technology.

https://www.nsf.gov/mps/phy/nggw/mpsac_nggw_subcommittee_report_2024-03-23.pdf

Interestingly, it also stated:

U.S. leadership. The European GW science community, with support from their funding
agencies, is further ahead in their planning for their ngGW facility (ET). As LIGO is
approaching its currently-targeted design sensitivity (A+), it is imperative that the U.S., the
current leader in this nascent field of GW astrophysics with breakthrough discoveries,
seriously plan for our ngGW facility in a carefully-considered multi-step, multi-faceted way.

ET here stands for "Einstein Telescope", the joint-European concept for the next generation GW detector somewhere in Europe (AFAIK, no site has been choosen, yet).I would not be surprised if Europen calls for funding of ET basically make the same statement, jsut reversed: with thge US now on a clear trajectory to implement Cosmic Explorer, it's important to expedite efforts to make ET a reality.

https://www.einsteintelescope-emr.eu/en/

I suspect that much of the talk about "leadership" is more meant for the politicians who will (hopefully) provide the funds. The simple truth is that to do optimal science, you need at least 3 different sites, ideally of ball-park comparable sensitivity and on sites all over the planet, operating at the same time. No single country can do that by itself.So if either the US or Europe should scale back their efforts, the other side will lose as well. Synergy,

In other HEN-related news, the Kilonova Catcher citizen science project ( http://kilonovacatcher.in2p3.fr/  )  is keeping a close watch of x-ray transients detected by the new "Einstein Probe" space telescope. Please subscribe (see URL above) to join the hunt. The alerts are very time-critical and deserve a fast response, so it doesn't make much sense to discuss them here in this forum, instead the Slack-channel of KNC is the place to coordinate in real time. For notable events, the results will usually be published in a GCN circular and/or ATel like these

https://www.astronomerstelegram.org/?read=16531

https://www.astronomerstelegram.org/?read=16674

Finally, the HEN section was featured in A AAVSO webinar recently. The video doesn't seem to available just yet, but should be soon-ish, and then will be listed here: https://www.youtube.com/@AAVSOHQ/videos

As I mentioned in the mini-talk, I'd like to hear opionions about whether we should start new, additional ways of coming together in the HEN section. Other sections have introduced (google-groups) mailing lists and/or are holding regular zoom meetings. If there is interest in this, we certainly can do this as well.

Any opioons on this? ==> Please reply to this message.

Clear Skies

HB