The IPO launch result has left Big Hit Entertainment with a market value of more than US$8bn.

While interest in the flotation was high, there are concerns about Big Hit's perceived over-reliance on BTS, which accounts for 88% of its revenue.

There are concerns that the group's upcoming military service could also affect profitability.

Interest in the Initial Public Offering (IPO) was high, with almost half of Big Hit's 10 million tradable shares changing hands.

When trading began, Big Hit shares initially jumped to 270,000 Korean won ($235; £180). Although the shares then slipped back to close at 258,000 won, that was still about 90% higher than the initial IPO price.

The debut will make Big Hit's chief executive Bang Si-hyuk a billionaire.

It will also be worth millions to each of BTS's seven members, who were each given more than 63,000 shares.

At the listing ceremony, Mr Bang said the company planned to create "new value chains" to ensure the company's continued growth.

Big Hit Entertainment has bought up several other smaller labels in the past year, but BTS is still by far their biggest money maker.

Why do investors think BTS is a good bet?

BTS is one of the world's biggest acts, and many investors feel it's a safe bet that they will continue to make money for Big Hit.

Even in the age of digital streaming, their album sales are strong, and their shows sell out within minutes.

They also have a large number of advertising partnerships for products ranging from cars to cosmetics.

Military service

Despite this, some are worried that Big Hit's greatest strength - BTS - is also its greatest vulnerability.

By law, all able-bodied Korean men aged between 18 and 28 must serve in the country's military for 20 months.

All seven members of BTS will be required to sign up within the next few years, although there has been some discussion of allowing them to defer.

It is not yet clear how a break for military service might affect Big Hit's profitability.

Topping the US charts is a rare feat for any group that mostly doesn't sing in English.

Only 20 predominantly non-English tracks have ever cracked the top ten in its 60-year history.

Three of them are BTS tracks, and now they've finally had a number one single (although it was sung in English). US fans have responded in droves to BTS's infectious, danceable pop - and to their willingness to engage seriously about issues affecting their fans

"BTS always emphasizes the importance of kindness and compassion and talk about many of the same experiences, fears, and dreams that we all experience at some point in our life.

This brings so many fans, like myself, a sense of comfort and belonging," says Michelle Gutierrez, a 26 year-old graduate student from Texas, who is hoping to invest when shares becomes available in the US.

Number one debut?

About 20% of its shares have been offered to investors, raising $822m - originally valuing the company at over $4bn pre-launch.

The seven BTS members will receive 68,385 shares each, making them all very wealthy, although they already make lots of money.

According to Forbes, they earned $50m last year, with their road show grossing $170m.

But by some measures, their contribution to South Korea's economy far bigger.

One recent study by the tourism ministry and a government tourism institute calculated that their single Dynamite would generate a staggering $2.4bn in economic activity and nearly 8,000 new jobs - coming not just from direct sales but from sales of cosmetics as well as food and drinks.

The appeal for investors is simple: BTS are a global pop music juggernaut, and they're likely to deliver returns. Dynamite was so popular that it was the first ever video to clock up 100 million YouTube views within 24 hours.

Album sales are strong, even in the age of digital streaming. Live shows sell out in minutes, and BTS have amassed a huge number of brand partnerships, ranging from cars to cosmetics.

It's rare, however, that fans have an opportunity to buy into a specific musical act. David Bowie issued "Bowie Bonds" in 1997, which gave investors a cut of the royalties from his catalogue.

But even then, they were snapped up for $55m by Prudential Financial rather than being offered to ordinary fans.

More often, investors buy into firms owning the publishing rights to a stable of musicians. In the case of Big Hit, 88% of its revenues came from BTS in the first half of this year.

So investors and fans alike see an investment in one as an investment in the other.

That's given some fans pause.

Sure beats packing the shelves at Coles for a living!