Spotting a 'New Star' in the night sky
Hopefully, what you will see is a nova, a type of temporary 'new star'
Did you get to observe the total solar eclipse on Monday, April 8? Pretty impressive, wasn't it? However, if you think that was a oncein-a-lifetime event (and no doubt, for some people it was), how about having a look for another, even rarer, celestial event? For many of us, it, too, will be a once-in-alifetime event.
Unlike the total solar eclipse, this event will be visible to everyone in the Northern Hemisphere. Imagine the thrill of being among the first people to spot a "new star" in the night sky. Actually, you will not be seeing a new star per se; what you will, hopefully, see is a nova, a type of temporary "new star."
A nova occurs when one star of a binary two-star system has gravitationally syphoned off enough stellar material from the other star in the system that it explodes and dramatically increases in brightness, sufficient enough that it can be seen shining brightly like a "new star" for a period of time, before slowly fading away.
EVOLUTIONARY STATE OF A STAR
If you recall from my earlier articles on stellar evolution and types, a white dwarf star is the final evolutionary state of a star that does not have, at the end of its life, enough mass to become either a neutron star or a black hole. It is a dense stellar core remnant with low luminosity. The material within a white dwarf star no longer undergoes fusion reactions, and, having no energy source, and unable to support itself by the heat from fusion against its own gravity, it collapses into an extremely dense body.
A red giant is a massive, luminous star of low-tomedium mass that, having exhausted its core hydrogen supply, has begun thermonuclear fusion of the hydrogen shell surrounding its core. The outer atmosphere of the red giant becomes inflated, its radius expanding outward. The low temperature of this outer shell gives these giant stars their classical orange-red appearance. An example of a red giant star is Arcturus in the constellation of Bootes the Herdsman.
RED VS. WHITE
If a white dwarf and a red giant are the components of a binary, two-star system, and their shared orbital period is sufficiently close (within the range of several days to one day), the gravity of the denser white dwarf distorts the red giant's outer atmosphere, and matter from the red giant (referred to as the "secondary") is transferred to the white dwarf (referred to as the "primary").
Over time, this infalling matter accumulates as an accretion disk around the white dwarf, and when sufficient in volume falls from the inner edge of the accretion disk onto the surface of the white dwarf.
When the density and temperature at the bottom of the accumulated layer reaches a critical level, the layer, composed primarily of hydrogen, explodes in a cataclysmic eruption that blasts the layer off the white dwarf, in the process forming a luminous envelope seen as visible light that increases the primary's brightness by a factor on a scale of 50,000 times, thereby creating a nova or "new star".
REOCCURRING PROCESS
The highly luminous envelope, depending on the amount of mnatedrial blown off, is, however, a transient astronomical event, typically lasting only for several days, weeks, or months.
If the white dwarf and the red giant remain intact, the whole process typically begins again, and can repeat multiple times. Such repeating nova events are referred to as "recurrent novae", which follow the same processes as a classical nova except that the fusion ignition is repetitive as the primary again begins to feed on the atmosphere of the secondary.
Examples of recurrent novae include GK Persei (Nova Persei 1901), DQ Herculis (Nova herculis 1934), and V1974 Cygni (Nova Cygni 1992).
HOW TO BEST OBSERVE FORTHCOMING NOVA
The forthcoming nova will be located in the constellation of Corona Borealis, the U-shaped constellation to the left of the kite-shaped constellation of Bootes - the Herdsman, visible in the evening spring sky.
If you first locate the Big Dipper asterism in Ursa Major - the Great Bear, and follow the arc of the dipper's handle downward, the first really bright star you will come to will be Arcturus, the brightest star in Bootes. Corona Borealis is located to the left of Bootes, between this constellation and Hercules - the Giant. The constellation of Corona Borealis was named for the crown that Princess Ariadne, the daughter of King Midas of Phrygia, wore when she married Dionysus, the Greek god of wine and theater, who then placed the crown in the heavens to commemorate their wedding.
This constellation is best observed when it is highest in the night sky overhead by about midnight in May. However, the constellation will slowly drift to the westward as spring progresses and the summer months arrive, and may prove challenging to see in the late evening western sky in August and September.
NOVA PHENOMENON
The anticipated nova in Corona Borealis will be the star T Coronae Borealis, located to the lower right of the star Epsilon Corona Borealis (the second star down on the left side of the crown). The nova itself is expected at any time between now and September. Hopefully, the nova will occur while Corona Borealis is still readily observable in the night sky. The nova phenomenon of T Coronae Borealis occurs approximately every 80 years, and is predicted to reach mag. +2.0.
If you are interested in locating T Coronae Borealis, type in "detailed map of T Coronae Borealis" in Google. On the page of maps that appears, the Sky and Telescope map (far right, second from top) is the best map to show the location of T Coronae Borealis. Use your binoculars or telescope to familiarize yourself with the stars in the area of T Coronae Borealis; this should at least provide you with the general idea of which star to focus on as you watch for the nova over the next few months. The map will also give you the magnitude of the stars in the crown.
Pay particular attention to the star Gemma (third star downward on the right side of the crown); at mag. +2,2, this star will give you an idea, by comparison, of how bright T Coronae Borealis is expected to get at the peak of the nova, although it could possibly get brighter.
You can also familiarize yourself with the magnitudes of the stars in the Big Dipper as additional reference stars. Hopefully, the nova of T Coronae Borealis will reach naked eye visibility in September.
THIS WEEK'S SKY
This is not a good week if you are a planet-watcher. None of the bright planets are visible in the night sky this week; they are all either on or below the horizon, or too close to the Sun to be observed.
Mercury (mag. +5.3, in Pisces - the Fish) is 2 degrees below the eastern horizon at dawn, and sits just on the horizon at dawn on May 5.
Venus (mag. -3.9, in Pisces) is only 1 degree below the eastern horizon at dawn on April 29, but drops another degree to 2 degrees below the horizon by the 5th of May.
Mars (mag. +1.2, in Aquarius) fares not better, at only 4 degrees above the southeast horizon on April 29, and only slightly better, at 5 degrees above the horizon, by May 5.
Even bright Jupiter (mag. -2.0, in Aries - the Ram), which has sailed the celestial night sky alone for the past week or so, is not to be seen, visible only 6 degrees above the western horizon at dusk to start this week, sitting at only 2 degrees above the horizon at dusk at the end of the week.
Saturn (mag. +1.2, in Aquarius) sits 8 degrees above the southeast horizon at dawn on the 29th, and only reaches 10 degrees above the horizon on the 5th.
Uranus (mag. +5.8, Aries), 12 degrees from the Sun, and Neptune (mag. +8.0, in Pisces) 1 degree below the southeast horizon at dawn, are also not observable this week.
Comet P12/pons-brooks is still observable in binoculars and telescopes (and possibly with the naked eye under a dark sky) in the constellation of Taurus - the Bull. The comet is currently at mag. +4.55 (Apr. 29), but will slowly continue to fade (mag. 4.78 by May 5) as it recedes farther from the Sun.
Until next week, clear skies.