February 22, 2018

Astro-Challenge: Spy a Microquasar.

So, you’ve seen everything the night sky has to offer? You say you’ve seen all breeds of eclipses and deep sky objects, and have grown tired of showing the neighbors Saturn and the Ring Nebula? Well, we’ve got a challenge for you. This week’s object will require dark skies, a good finder chart, and a generous aperture telescope.  About 4 degrees northwest of the 3rd magnitude star Delta Aquilae lies +14.1 magnitude SS 433.

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15.05.10: A Speedy Binary.

Think that new Ducati in your garage is fast? Let me introduce you to HM Cancri. An unassuming +21 magnitude binary in the constellation Cancer, HM Cancri is comprised of two white dwarfs locked in a tight embrace. In fact, this binary system has the shortest orbital period known, handily knocking down distant contender V407 Vulpeculae with its “stately” 9.5 minute orbit. The facts are dizzying; the pair weigh in at 0.5 and 0.25 solar masses respectively, are about 24,000 miles apart (think geosynchronous orbit!) and revolve around each other in 5.4 minutes, about the time you hopefully spend glancing over this blog before returning to Facebook.  Get your calculators out; this makes orbital velocity for the pair an impressive 230 miles per second! Discovered in 1999, Observations using the Keck telescope have upheld HM Cancri’s record holding status by analyzing opposing spectral shifts of ionized helium as the two stars whirl about. This rules out other candidates such as a single neutron star.  Such a system must have had a very unique history, perhaps starting as a pair of Sun-like stars that later spiraled in. Will the two merge one day? Conservation of angular momentum cannot fully explain what we see as the system is speeding up; perhaps more accreting matter is present than we currently account for. The pair are approaching each other by about two feet per day, and of course, relativity comes into play in such an extreme system. Clearly, something interesting is occurring in this system. HM Cancri is also a strong x-ray source, and should generate copious amounts of gravity waves, especially in the event of a merger. Said waves may be within the realm of Advanced LIGO, due to come online in 2014, or LISA, ESA’s proposed Laser Interferometer Space Antenna. HM Cancri lies about 16,000 light years distant, and may be the strongest source of gravity waves in our galaxy.