Weird Object: Pular Planet

Pulsar: 

Seven years earlier, astronomers Aleksander Wolszczan and Dale Frail announced they had found not one but two planets — and these orbited the oddest kind of star in the universe, a millisecond pulsar. 

Its name is PSR B1257+12, and it lies in the constellation Virgo the Virgin at a distance of 980 light-years. It spins 161 times a second and, like all pulsars, is a neutron star, the smallest and densest visible object in the universe. 

No telescope was used in the discovery — at least not one that gathers visible light. Instead, the radio telescope in Arecibo, Puerto Rico, with its 1,000-foot (305 meters) collecting area, carefully monitored radio signals from pulsars. Electromagnetic energy streaming away from their magnetic poles sweeps around like a lighthouse beam, producing flashes with each rotation.

These super-collapsed neutron stars are always less than 20 miles (32 kilometers) wide, with wild amusement park spins of dozens or even hundreds of rotations per second. What’s valuable for astrophysicists isn’t the ultra-fast spin but the Teutonic regularity. If the rate changes, something interesting must be going on. 

In 1991, astronomers detected just such a changing period in PSR B1257+12’s spin and got to work deciphering why the signals were alternately delayed and then advanced. Obviously something was yanking the tiny star back and forth in a predictable fashion. What size object, and at what orbital distance and period, would do the job? In this case, the exact fit could be achieved if this pulsar is orbited by two small nearby planets; later refinements added a third definite planet, as well as a potential ultra-teensy fourth.

Of the three definite pulsar planets, one weighs 1/50 Earth mass (not too dissimilar to our Moon), while the other two have about 4 Earth masses apiece. The “years” it takes this trio to orbit their pulsar sun last 25, 67, and 98 Earth days. And there you have the first-ever planets found since Neptune’s discovery in 1846. (We can’t count Pluto anymore now that it’s considered a dwarf planet. See object 39 on our list.)