STARGAZING: Dim stars last the longest

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, Penticton.

Stars are really interesting things. They provide heat and light, making life possible on our world, and probably other worlds too.

In making that heat and light, they also produce as waste products the elements needed to make worlds and living creatures. Thatís how we got from a universe that was once almost entirely made up of hydrogen gas to the universe we live in and see around us today.

Even the most casual look at the night sky shows that some stars look a lot brighter than others. They are also different. Stars differ in apparent brightness because some are much closer to us than others, and also because some are intrinsically much brighter than others.

We describe the total energy output from stars in terms of luminosity. We say the Sun has a luminosity of one, so a star with a luminosity of 100 radiates 100 times as much energy as the Sun. If we know the distance of a star and measure how bright it looks in the sky, we can calculate its luminosity. By carefully measuring its colour, we can estimate its temperature.

Just knowing these two numbers for a star tells us a lot. In the early 20th Century, two astronomers: Danish astronomer Ejnar Hertzsprung and American astronomer Henry Norris Russell, working totally independently, plotted the luminosities of hundreds of stars against their temperatures. What they found was really intriguing. Most of the stars by far fell onto a band extending from the top left (bright, hot) of the diagram to the bottom right (dim, cool). That band is now known as the Main Sequence.

Stars drop onto the Main Sequence soon after they are born, at a location depending on their mass, stay there for most of their lives, shining fairly steadily, and then move off it when they get old and start to run out of fuel.

In human terms a star’s life is something like growing up to age 25 in the first two or three years of life, and then aging slowly so that after 80 years of life your physical age is around 30, and then going downhill rapidly.Stars shine because the weight of overlying material compresses and heats their cores to the point where nuclear fusion occurs. A high-mass star will have a more highly-compressed core, while the compression in a low mass star will be much less.

The rate of energy production is extremely sensitive to this. A star with twice the mass of the Sun will produce energy at about 16 times the rate. The Sun will sit on the Main Sequence, providing us with a fairly steady supply of heat and light for roughly eight billion years. A two solar mass star will only be able to do this for one billion years. If our Earth were orbiting such a star, things would have ended for the Earth while the most advanced living creatures were still single-celled things living in the sea. A 10 solar mass star will radiate energy at roughly 10,000 times the rate the Sun does, and will be in trouble in less than 10 million years. So there is really not much point in looking for complex life forms on planets orbiting stars two or more times the Sun’s mass.

A star half the Sun’s mass will spend eight times longer on the Main Sequence than the Sun does, giving lots of time for life to appear on its planets. Even less massive, red dwarf stars are so stingy with their energy production they might last as long as the universe. Dim stars last longest.

For any star there is a Goldilocks Zone: the range of distances where planets would have the right temperatures for life. For a dim star, that zone lies close to the star and is narrow, reducing the chance of planets being in it. For bright stars the zone is more distant and broader. Stars like the Sun are a compromise between long life and a Goldilocks Zone big enough to contain planets.

Jupiter is descending in the west, and Mars and Saturn lie in the southern sky. Mars is the bright one; Saturn is fainter and to Mars’ left. The Moon will be New on the July 4.

Ken Tapping is an astronomer with the National Research Council’s Dominion Radio Astrophysical Observatory, Penticton.


Just Posted

James Miller, the managing editor at the Penticton Herald, has been voted in for Jake Kimberley’s vacated council seat. (Submitted)
James Miller elected as Penticton city councillor

Penticton also voted yes to allowing up to 25 years for a Skaha Marina contract

The Eyes of the Tigers on the 2021 Beer Run on June 19. (Brennan Phillips - Western News)
Penticton Beer Runners take trip around local beaches and brews

Over 160 people signed up to come back after the 2020 run was cancelled

There was high voter turnout for the first of three advance voting days for the Penticton city by-election.
Penticton city by-election general voting day is today, June 19

737 voters on June 9 in comparison to 2018 general election, which had 1,001 on first day

Police are asking for public assistance in locating Anthony Graham who has been charged with the murders of Kamloops brothers Carlo and Erick Fryer. (RCMP photo)
2 Penticton-area men charged with Kamloops brothers’ double homicide

Brothers Erick and Carlo Fryer were found deceased in May in Naramata

(File photo)
Penticton not holding Canada Day activities out of respect for Indigenous people

Cities across B.C. are cancelling the holiday after an increased spotlight on Canada’s dark history

Marco Mendicino, Minister of Immigration, Refugees and Citizenship during a press conference in Ottawa on Thursday, May 13, 2021. THE CANADIAN PRESS/Sean Kilpatrick
Canada to welcome 45,000 refugees this year, says immigration minister

Canada plans to increase persons admitted from 23,500 to 45,000 and expedite permanent residency applications

Emily Steele holds up a collage of her son, 16-year-old Elijah-Iain Beauregard who was stabbed and killed in June 2019, outside of Kelowna Law Courts on June 18. (Aaron Hemens/Capital News)
Kelowna woman who fatally stabbed Eli Beauregard facing up to 1.5 years of jail time

Her jail sentence would be followed by an additional one to 1.5 years of supervision

Cpl. Scott MacLeod and Police Service Dog Jago. Jago was killed in the line of duty on Thursday, June 17. (RCMP)
Abbotsford police, RCMP grieve 4-year-old service dog killed in line of duty

Jago killed by armed suspect during ‘high-risk’ incident in Alberta

The George Road wildfire near Lytton, B.C., has grown to 250 hectares. (BC Wildfire Service)
B.C. drone sighting halts helicopters fighting 250 hectares of wildfire

‘If a drone collides with firefighting aircraft the consequences could be deadly,’ says BC Wildfire Service

A dose of the Pfizer-BioNTech COVID-19 vaccine is pictured at a vaccination site in Vancouver Thursday, March 11, 2021. THE CANADIAN PRESS/Jonathan Hayward
NACI advice to mix vaccines gets varied reaction from AstraZeneca double-dosers

NACI recommends an mRNA vaccine for all Canadians receiving a second dose of a COVID-19 vaccine

A aerial view shows the debris going into Quesnel Lake caused by a tailings pond breach near the town of Likely, B.C., Tuesday, Aug. 5, 2014. THE CANADIAN PRESS/Jonathan Hayward
Updated tailings code after Mount Polley an improvement: B.C. mines auditor

British Columbia’s chief auditor of mines has found changes to the province’s requirements for tailings storage facilities

Starting in 2022, the Columbia Shuswap Regional District is extending dog control to the entire Electoral Area D. (Stock photo)
Dog control bylaw passes in Shuswap area despite ‘threatening’ emails

CSRD board extending full dog control in Electoral Area D starting next year

A North Vancouver man was arrested Friday and three police officers were injured after a 10-person broke out at English Bay on June 19, 2021. (Youtube/Screen grab)
Man arrested, 3 police injured during 10-person brawl at Vancouver beach

The arrest was captured on video by bystanders, many of whom heckled the officers as they struggled with the handcuffed man

Most Read